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 $232.48   9.338%   $254.189   $254.19   $254.20   $254.20  
  Purchase #2 $91.50   3.482%   $94.686   $94.69   $94.70   $94.70  
  Purchase #3 $96.74   12.539%   $108.8702   $108.87   $108.85   $108.90  
  Purchase #4 $142.91   5.826%   $151.2359   $151.24   $151.25   $151.20  
  Purchase #5 $177.97   8.197%   $192.5582   $192.56   $192.55   $192.60  
  Purchase #6 $120.78   4.157%   $125.8008   $125.80   $125.80   $125.80  
  Purchase #7 $35.90   10.438%   $39.6472   $39.65   $39.65   $39.60  
  7 purchase totals = $898.28       $966.9873   $967.00   $967.00   $967.00