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 $207.52   8.212%   $224.5615   $224.56   $224.55   $224.60  
  Purchase #2 $245.80   4.414%   $256.6496   $256.65   $256.65   $256.60  
  Purchase #3 $69.99   9.552%   $76.6754   $76.68   $76.70   $76.70  
  Purchase #4 $156.76   5.673%   $165.653   $165.65   $165.65   $165.70  
  Purchase #5 $46.79   11.844%   $52.3318   $52.33   $52.35   $52.30  
  Purchase #6 $141.52   6.389%   $150.5617   $150.56   $150.55   $150.60  
  Purchase #7 $61.65   12.753%   $69.5122   $69.51   $69.50   $69.50  
  7 purchase totals = $930.03       $995.9452   $995.94   $995.95   $996.00