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 $236.78   3.778%   $245.7255   $245.73   $245.75   $245.70  
  Purchase #2 $127.27   11.534%   $141.9493   $141.95   $141.95   $141.90  
  Purchase #3 $245.52   4.643%   $256.9195   $256.92   $256.90   $256.90  
  Purchase #4 $41.64   11.440%   $46.4036   $46.40   $46.40   $46.40  
  Purchase #5 $199.34   13.844%   $226.9366   $226.94   $226.95   $226.90  
  Purchase #6 $124.77   11.452%   $139.0587   $139.06   $139.05   $139.10  
  Purchase #7 $18.56   6.273%   $19.7243   $19.72   $19.70   $19.70  
  7 purchase totals = $993.88       $1,076.7175   $1,076.72   $1,076.70   $1,076.60