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 $159.71   11.127%   $177.4809   $177.48   $177.50   $177.50  
  Purchase #2 $32.59   12.746%   $36.7439   $36.74   $36.75   $36.70  
  Purchase #3 $43.95   10.826%   $48.708   $48.71   $48.70   $48.70  
  Purchase #4 $72.75   4.247%   $75.8397   $75.84   $75.85   $75.80  
  Purchase #5 $207.94   10.823%   $230.4453   $230.45   $230.45   $230.40  
  Purchase #6 $98.54   3.584%   $102.0717   $102.07   $102.05   $102.10  
  Purchase #7 $153.66   4.605%   $160.736   $160.74   $160.75   $160.70  
  7 purchase totals = $769.14       $832.0255   $832.03   $832.05   $831.90