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 $56.38   10.766%   $62.4499   $62.45   $62.45   $62.40  
  Purchase #2 $62.39   7.258%   $66.9183   $66.92   $66.90   $66.90  
  Purchase #3 $140.68   4.543%   $147.0711   $147.07   $147.05   $147.10  
  Purchase #4 $214.37   5.306%   $225.7445   $225.74   $225.75   $225.70  
  Purchase #5 $243.45   12.390%   $273.6135   $273.61   $273.60   $273.60  
  Purchase #6 $45.55   4.606%   $47.648   $47.65   $47.65   $47.60  
  Purchase #7 $98.49   7.151%   $105.533   $105.53   $105.55   $105.50  
  7 purchase totals = $861.31       $928.9783   $928.97   $928.95   $928.80