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 $141.66   6.272%   $150.5449   $150.54   $150.55   $150.50  
  Purchase #2 $45.32   6.526%   $48.2776   $48.28   $48.30   $48.30  
  Purchase #3 $60.54   5.372%   $63.7922   $63.79   $63.80   $63.80  
  Purchase #4 $221.41   7.310%   $237.5951   $237.60   $237.60   $237.60  
  Purchase #5 $241.97   9.502%   $264.962   $264.96   $264.95   $265.00  
  Purchase #6 $200.85   4.480%   $209.8481   $209.85   $209.85   $209.80  
  Purchase #7 $10.27   9.537%   $11.2494   $11.25   $11.25   $11.20  
  7 purchase totals = $922.02       $986.2693   $986.27   $986.30   $986.20