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 $46.89   4.538%   $49.0179   $49.02   $49.00   $49.00  
  Purchase #2 $55.43   13.545%   $62.938   $62.94   $62.95   $62.90  
  Purchase #3 $125.86   9.455%   $137.7601   $137.76   $137.75   $137.80  
  Purchase #4 $26.38   3.742%   $27.3671   $27.37   $27.35   $27.40  
  Purchase #5 $87.51   8.805%   $95.2153   $95.22   $95.20   $95.20  
  Purchase #6 $239.84   10.850%   $265.8626   $265.86   $265.85   $265.90  
  Purchase #7 $208.57   13.547%   $236.825   $236.83   $236.85   $236.80  
  7 purchase totals = $790.48       $874.9860   $875.00   $874.95   $875.00