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 $197.97   13.625%   $224.9434   $224.94   $224.95   $224.90  
  Purchase #2 $129.37   6.444%   $137.7066   $137.71   $137.70   $137.70  
  Purchase #3 $96.55   4.485%   $100.8803   $100.88   $100.90   $100.90  
  Purchase #4 $190.45   11.713%   $212.7574   $212.76   $212.75   $212.80  
  Purchase #5 $102.48   5.636%   $108.2558   $108.26   $108.25   $108.30  
  Purchase #6 $216.92   10.172%   $238.9851   $238.99   $239.00   $239.00  
  Purchase #7 $119.77   13.682%   $136.1569   $136.16   $136.15   $136.20  
  7 purchase totals = $1,053.51       $1,159.6855   $1,159.70   $1,159.70   $1,159.80