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 $68.42   11.467%   $76.2657   $76.27   $76.25   $76.30  
  Purchase #2 $50.88   6.806%   $54.3429   $54.34   $54.35   $54.30  
  Purchase #3 $67.97   4.487%   $71.0198   $71.02   $71.00   $71.00  
  Purchase #4 $210.97   6.272%   $224.202   $224.20   $224.20   $224.20  
  Purchase #5 $84.85   3.657%   $87.953   $87.95   $87.95   $88.00  
  Purchase #6 $43.93   12.437%   $49.3936   $49.39   $49.40   $49.40  
  Purchase #7 $74.71   6.832%   $79.8142   $79.81   $79.80   $79.80  
  7 purchase totals = $601.73       $642.9912   $642.98   $642.95   $643.00