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 $57.38   8.759%   $62.4059   $62.41   $62.40   $62.40  
  Purchase #2 $141.94   7.267%   $152.2548   $152.25   $152.25   $152.30  
  Purchase #3 $228.44   13.149%   $258.4776   $258.48   $258.50   $258.50  
  Purchase #4 $88.75   7.815%   $95.6858   $95.69   $95.70   $95.70  
  Purchase #5 $112.26   12.521%   $126.3161   $126.32   $126.30   $126.30  
  Purchase #6 $119.93   10.671%   $132.7277   $132.73   $132.75   $132.70  
  Purchase #7 $241.28   13.220%   $273.1772   $273.18   $273.20   $273.20  
  7 purchase totals = $989.98       $1,101.0451   $1,101.06   $1,101.10   $1,101.10