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 $63.48   10.228%   $69.9727   $69.97   $69.95   $70.00  
  Purchase #2 $78.62   13.158%   $88.9648   $88.96   $88.95   $89.00  
  Purchase #3 $231.97   5.209%   $244.0533   $244.05   $244.05   $244.10  
  Purchase #4 $25.65   7.106%   $27.4727   $27.47   $27.45   $27.50  
  Purchase #5 $125.47   13.824%   $142.815   $142.82   $142.80   $142.80  
  Purchase #6 $98.94   5.664%   $104.544   $104.54   $104.55   $104.50  
  Purchase #7 $179.82   6.488%   $191.4867   $191.49   $191.50   $191.50  
  7 purchase totals = $803.95       $869.3092   $869.30   $869.25   $869.40