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 $234.65   5.115%   $246.6523   $246.65   $246.65   $246.70  
  Purchase #2 $59.60   12.815%   $67.2377   $67.24   $67.25   $67.20  
  Purchase #3 $215.26   9.345%   $235.376   $235.38   $235.40   $235.40  
  Purchase #4 $208.77   13.625%   $237.2149   $237.21   $237.20   $237.20  
  Purchase #5 $61.43   10.448%   $67.8482   $67.85   $67.85   $67.80  
  Purchase #6 $178.38   8.780%   $194.0418   $194.04   $194.05   $194.00  
  Purchase #7 $207.32   10.533%   $229.157   $229.16   $229.15   $229.20  
  7 purchase totals = $1,165.41       $1,277.5279   $1,277.53   $1,277.55   $1,277.50