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 $59.37   5.414%   $62.5843   $62.58   $62.60   $62.60  
  Purchase #2 $117.63   3.318%   $121.533   $121.53   $121.55   $121.50  
  Purchase #3 $26.53   12.238%   $29.7767   $29.78   $29.80   $29.80  
  Purchase #4 $52.62   11.662%   $58.7565   $58.76   $58.75   $58.80  
  Purchase #5 $110.37   9.717%   $121.0947   $121.09   $121.10   $121.10  
  Purchase #6 $176.32   3.671%   $182.7927   $182.79   $182.80   $182.80  
  Purchase #7 $232.96   7.630%   $250.7348   $250.73   $250.75   $250.70  
  7 purchase totals = $775.80       $827.2727   $827.26   $827.35   $827.30