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 $233.98   5.243%   $246.2476   $246.25   $246.25   $246.20  
  Purchase #2 $65.34   4.484%   $68.2698   $68.27   $68.25   $68.30  
  Purchase #3 $204.37   10.193%   $225.2014   $225.20   $225.20   $225.20  
  Purchase #4 $246.71   5.672%   $260.7034   $260.70   $260.70   $260.70  
  Purchase #5 $250.56   10.144%   $275.9768   $275.98   $276.00   $276.00  
  Purchase #6 $101.39   13.646%   $115.2257   $115.23   $115.25   $115.20  
  Purchase #7 $51.25   9.623%   $56.1818   $56.18   $56.20   $56.20  
  7 purchase totals = $1,153.60       $1,247.8065   $1,247.81   $1,247.85   $1,247.80