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 $57.47   9.652%   $63.017   $63.02   $63.00   $63.00  
  Purchase #2 $135.94   7.762%   $146.4917   $146.49   $146.50   $146.50  
  Purchase #3 $241.87   12.117%   $271.1774   $271.18   $271.20   $271.20  
  Purchase #4 $222.28   3.370%   $229.7708   $229.77   $229.75   $229.80  
  Purchase #5 $193.98   12.706%   $218.6271   $218.63   $218.65   $218.60  
  Purchase #6 $201.39   12.286%   $226.1328   $226.13   $226.15   $226.10  
  Purchase #7 $95.56   5.381%   $100.7021   $100.70   $100.70   $100.70  
  7 purchase totals = $1,148.49       $1,255.9189   $1,255.92   $1,255.95   $1,255.90