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 $229.94   6.207%   $244.2124   $244.21   $244.20   $244.20  
  Purchase #2 $132.70   12.811%   $149.7002   $149.70   $149.70   $149.70  
  Purchase #3 $44.55   12.374%   $50.0626   $50.06   $50.05   $50.10  
  Purchase #4 $126.77   5.271%   $133.452   $133.45   $133.45   $133.50  
  Purchase #5 $19.28   11.281%   $21.455   $21.46   $21.45   $21.50  
  Purchase #6 $76.27   10.392%   $84.196   $84.20   $84.20   $84.20  
  Purchase #7 $121.76   10.441%   $134.473   $134.47   $134.45   $134.50  
  7 purchase totals = $751.27       $817.5512   $817.55   $817.50   $817.70