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 $19.96   7.456%   $21.4482   $21.45   $21.45   $21.40  
  Purchase #2 $207.86   7.803%   $224.0793   $224.08   $224.10   $224.10  
  Purchase #3 $48.71   3.379%   $50.3559   $50.36   $50.35   $50.40  
  Purchase #4 $161.69   8.478%   $175.3981   $175.40   $175.40   $175.40  
  Purchase #5 $57.95   5.790%   $61.3053   $61.31   $61.30   $61.30  
  Purchase #6 $79.90   7.470%   $85.8685   $85.87   $85.85   $85.90  
  Purchase #7 $152.69   11.543%   $170.315   $170.32   $170.30   $170.30  
  7 purchase totals = $728.76       $788.7703   $788.79   $788.75   $788.80