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 $65.95   13.338%   $74.7464   $74.75   $74.75   $74.70  
  Purchase #2 $234.25   6.662%   $249.8557   $249.86   $249.85   $249.90  
  Purchase #3 $70.92   12.232%   $79.5949   $79.59   $79.60   $79.60  
  Purchase #4 $112.36   5.420%   $118.4499   $118.45   $118.45   $118.40  
  Purchase #5 $138.49   8.590%   $150.3863   $150.39   $150.40   $150.40  
  Purchase #6 $116.86   6.417%   $124.3589   $124.36   $124.35   $124.40  
  Purchase #7 $243.77   5.830%   $257.9818   $257.98   $258.00   $258.00  
  7 purchase totals = $982.60       $1,055.3739   $1,055.38   $1,055.40   $1,055.40