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 $228.84   7.791%   $246.6689   $246.67   $246.65   $246.70  
  Purchase #2 $249.87   12.349%   $280.7264   $280.73   $280.75   $280.70  
  Purchase #3 $243.89   12.388%   $274.1031   $274.10   $274.10   $274.10  
  Purchase #4 $177.56   6.601%   $189.2807   $189.28   $189.30   $189.30  
  Purchase #5 $247.84   10.505%   $273.8756   $273.88   $273.90   $273.90  
  Purchase #6 $198.39   11.528%   $221.2604   $221.26   $221.25   $221.30  
  Purchase #7 $46.38   4.115%   $48.2885   $48.29   $48.30   $48.30  
  7 purchase totals = $1,392.77       $1,534.2036   $1,534.21   $1,534.25   $1,534.30