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 $54.71   6.794%   $58.427   $58.43   $58.45   $58.40  
  Purchase #2 $26.57   13.343%   $30.1152   $30.12   $30.10   $30.10  
  Purchase #3 $80.88   3.695%   $83.8685   $83.87   $83.85   $83.90  
  Purchase #4 $141.98   4.307%   $148.0951   $148.10   $148.10   $148.10  
  Purchase #5 $20.58   8.489%   $22.327   $22.33   $22.35   $22.30  
  Purchase #6 $164.71   13.112%   $186.3068   $186.31   $186.30   $186.30  
  Purchase #7 $190.49   3.518%   $197.1914   $197.19   $197.20   $197.20  
  7 purchase totals = $679.92       $726.3310   $726.35   $726.35   $726.30