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 $29.51   12.739%   $33.2693   $33.27   $33.25   $33.30  
  Purchase #2 $203.82   11.584%   $227.4305   $227.43   $227.45   $227.40  
  Purchase #3 $43.92   12.752%   $49.5207   $49.52   $49.50   $49.50  
  Purchase #4 $161.52   9.748%   $177.265   $177.27   $177.25   $177.30  
  Purchase #5 $184.64   9.191%   $201.6103   $201.61   $201.60   $201.60  
  Purchase #6 $69.45   6.838%   $74.199   $74.20   $74.20   $74.20  
  Purchase #7 $24.43   4.249%   $25.468   $25.47   $25.45   $25.50  
  7 purchase totals = $717.29       $788.7628   $788.77   $788.70   $788.80