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 $148.46   7.838%   $160.0963   $160.10   $160.10   $160.10  
  Purchase #2 $99.69   6.450%   $106.12   $106.12   $106.10   $106.10  
  Purchase #3 $132.44   8.228%   $143.3372   $143.34   $143.35   $143.30  
  Purchase #4 $36.54   9.388%   $39.9704   $39.97   $39.95   $40.00  
  Purchase #5 $183.71   3.613%   $190.3474   $190.35   $190.35   $190.30  
  Purchase #6 $72.52   11.713%   $81.0143   $81.01   $81.00   $81.00  
  Purchase #7 $16.32   5.785%   $17.2641   $17.26   $17.25   $17.30  
  7 purchase totals = $689.68       $738.1497   $738.15   $738.10   $738.10