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 $60.87   11.308%   $67.7532   $67.75   $67.75   $67.80  
  Purchase #2 $98.57   11.609%   $110.013   $110.01   $110.00   $110.00  
  Purchase #3 $125.68   11.164%   $139.7109   $139.71   $139.70   $139.70  
  Purchase #4 $240.93   12.646%   $271.398   $271.40   $271.40   $271.40  
  Purchase #5 $61.63   6.635%   $65.7192   $65.72   $65.70   $65.70  
  Purchase #6 $236.35   13.246%   $267.6569   $267.66   $267.65   $267.70  
  Purchase #7 $21.80   7.448%   $23.4237   $23.42   $23.40   $23.40  
  7 purchase totals = $845.83       $945.6749   $945.67   $945.60   $945.70