Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $238.53   3.231%   $246.2369   $246.24   $246.25   $246.20  
  Purchase #2 $163.50   12.638%   $184.1631   $184.16   $184.15   $184.20  
  Purchase #3 $181.43   10.591%   $200.6453   $200.65   $200.65   $200.60  
  Purchase #4 $159.77   12.432%   $179.6326   $179.63   $179.65   $179.60  
  Purchase #5 $94.48   12.460%   $106.2522   $106.25   $106.25   $106.30  
  Purchase #6 $149.37   3.161%   $154.0916   $154.09   $154.10   $154.10  
  Purchase #7 $169.67   12.610%   $191.0654   $191.07   $191.05   $191.10  
  7 purchase totals = $1,156.75       $1,262.0871   $1,262.09   $1,262.10   $1,262.10