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 $88.29   4.399%   $92.1739   $92.17   $92.15   $92.20  
  Purchase #2 $111.51   12.688%   $125.6584   $125.66   $125.65   $125.70  
  Purchase #3 $18.53   5.179%   $19.4897   $19.49   $19.50   $19.50  
  Purchase #4 $200.54   6.109%   $212.791   $212.79   $212.80   $212.80  
  Purchase #5 $137.93   3.155%   $142.2817   $142.28   $142.30   $142.30  
  Purchase #6 $87.63   7.570%   $94.2636   $94.26   $94.25   $94.30  
  Purchase #7 $14.91   13.737%   $16.9582   $16.96   $16.95   $17.00  
  7 purchase totals = $659.34       $703.6165   $703.61   $703.60   $703.80