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 $75.72   8.595%   $82.2281   $82.23   $82.25   $82.20  
  Purchase #2 $116.79   6.832%   $124.7691   $124.77   $124.75   $124.80  
  Purchase #3 $148.85   7.645%   $160.2296   $160.23   $160.25   $160.20  
  Purchase #4 $60.32   3.580%   $62.4795   $62.48   $62.50   $62.50  
  Purchase #5 $133.85   4.605%   $140.0138   $140.01   $140.00   $140.00  
  Purchase #6 $131.42   11.249%   $146.2034   $146.20   $146.20   $146.20  
  Purchase #7 $46.68   4.479%   $48.7708   $48.77   $48.75   $48.80  
  7 purchase totals = $713.63       $764.6943   $764.69   $764.70   $764.70