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 $66.85   8.809%   $72.7388   $72.74   $72.75   $72.70  
  Purchase #2 $230.43   8.131%   $249.1663   $249.17   $249.15   $249.20  
  Purchase #3 $59.34   8.854%   $64.594   $64.59   $64.60   $64.60  
  Purchase #4 $84.76   5.505%   $89.426   $89.43   $89.45   $89.40  
  Purchase #5 $195.50   4.661%   $204.6123   $204.61   $204.60   $204.60  
  Purchase #6 $96.32   8.792%   $104.7885   $104.79   $104.80   $104.80  
  Purchase #7 $187.78   5.214%   $197.5708   $197.57   $197.55   $197.60  
  7 purchase totals = $920.98       $982.8967   $982.90   $982.90   $982.90