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 $83.41   3.109%   $86.0032   $86.00   $86.00   $86.00  
  Purchase #2 $209.94   10.528%   $232.0425   $232.04   $232.05   $232.00  
  Purchase #3 $51.89   7.597%   $55.8321   $55.83   $55.85   $55.80  
  Purchase #4 $153.90   6.414%   $163.7711   $163.77   $163.75   $163.80  
  Purchase #5 $229.45   3.266%   $236.9438   $236.94   $236.95   $236.90  
  Purchase #6 $24.86   13.551%   $28.2288   $28.23   $28.25   $28.20  
  Purchase #7 $63.47   8.560%   $68.903   $68.90   $68.90   $68.90  
  7 purchase totals = $816.92       $871.7245   $871.71   $871.75   $871.60