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 $111.94   10.373%   $123.5515   $123.55   $123.55   $123.60  
  Purchase #2 $89.34   6.342%   $95.0059   $95.01   $95.00   $95.00  
  Purchase #3 $185.31   10.602%   $204.9566   $204.96   $204.95   $205.00  
  Purchase #4 $213.73   8.696%   $232.316   $232.32   $232.30   $232.30  
  Purchase #5 $63.79   4.223%   $66.4839   $66.48   $66.50   $66.50  
  Purchase #6 $236.29   4.367%   $246.6088   $246.61   $246.60   $246.60  
  Purchase #7 $54.25   6.813%   $57.9461   $57.95   $57.95   $57.90  
  7 purchase totals = $954.65       $1,026.8688   $1,026.88   $1,026.85   $1,026.90