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 $68.50   10.238%   $75.513   $75.51   $75.50   $75.50  
  Purchase #2 $43.90   4.853%   $46.0305   $46.03   $46.05   $46.00  
  Purchase #3 $116.42   10.494%   $128.6371   $128.64   $128.65   $128.60  
  Purchase #4 $152.36   3.656%   $157.9303   $157.93   $157.95   $157.90  
  Purchase #5 $61.69   12.177%   $69.202   $69.20   $69.20   $69.20  
  Purchase #6 $43.83   11.532%   $48.8845   $48.88   $48.90   $48.90  
  Purchase #7 $76.56   4.527%   $80.0259   $80.03   $80.05   $80.00  
  7 purchase totals = $563.26       $606.2233   $606.22   $606.30   $606.10