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 $243.54   9.646%   $267.0319   $267.03   $267.05   $267.00  
  Purchase #2 $195.64   13.726%   $222.4935   $222.49   $222.50   $222.50  
  Purchase #3 $44.79   13.433%   $50.8066   $50.81   $50.80   $50.80  
  Purchase #4 $190.57   4.700%   $199.5268   $199.53   $199.55   $199.50  
  Purchase #5 $131.95   10.743%   $146.1254   $146.13   $146.15   $146.10  
  Purchase #6 $197.40   3.786%   $204.8736   $204.87   $204.85   $204.90  
  Purchase #7 $246.34   13.404%   $279.3594   $279.36   $279.35   $279.40  
  7 purchase totals = $1,250.23       $1,370.2172   $1,370.22   $1,370.25   $1,370.20