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 $62.94   5.520%   $66.4143   $66.41   $66.40   $66.40  
  Purchase #2 $248.93   11.151%   $276.6882   $276.69   $276.70   $276.70  
  Purchase #3 $61.92   5.157%   $65.1132   $65.11   $65.10   $65.10  
  Purchase #4 $136.76   11.196%   $152.0716   $152.07   $152.05   $152.10  
  Purchase #5 $44.86   6.493%   $47.7728   $47.77   $47.75   $47.80  
  Purchase #6 $39.74   3.207%   $41.0145   $41.01   $41.00   $41.00  
  Purchase #7 $132.74   12.725%   $149.6312   $149.63   $149.65   $149.60  
  7 purchase totals = $727.89       $798.7058   $798.69   $798.65   $798.70