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 $135.41   10.529%   $149.6673   $149.67   $149.65   $149.70  
  Purchase #2 $59.84   9.492%   $65.52   $65.52   $65.50   $65.50  
  Purchase #3 $78.34   13.142%   $88.6354   $88.64   $88.65   $88.60  
  Purchase #4 $97.85   9.676%   $107.318   $107.32   $107.30   $107.30  
  Purchase #5 $71.58   4.571%   $74.8519   $74.85   $74.85   $74.90  
  Purchase #6 $246.40   12.819%   $277.986   $277.99   $278.00   $278.00  
  Purchase #7 $196.86   4.578%   $205.8723   $205.87   $205.85   $205.90  
  7 purchase totals = $886.28       $969.8509   $969.86   $969.80   $969.90