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 $40.35   7.398%   $43.3351   $43.34   $43.35   $43.30  
  Purchase #2 $213.30   9.804%   $234.2119   $234.21   $234.20   $234.20  
  Purchase #3 $236.69   3.837%   $245.7718   $245.77   $245.75   $245.80  
  Purchase #4 $33.41   3.735%   $34.6579   $34.66   $34.65   $34.70  
  Purchase #5 $50.49   13.501%   $57.3067   $57.31   $57.30   $57.30  
  Purchase #6 $35.25   13.267%   $39.9266   $39.93   $39.95   $39.90  
  Purchase #7 $154.40   11.269%   $171.7993   $171.80   $171.80   $171.80  
  7 purchase totals = $763.89       $827.0093   $827.02   $827.00   $827.00