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 $30.52   6.192%   $32.4098   $32.41   $32.40   $32.40  
  Purchase #2 $175.53   11.255%   $195.2859   $195.29   $195.30   $195.30  
  Purchase #3 $245.73   11.549%   $274.1094   $274.11   $274.10   $274.10  
  Purchase #4 $144.82   11.709%   $161.777   $161.78   $161.80   $161.80  
  Purchase #5 $162.25   6.844%   $173.3544   $173.35   $173.35   $173.40  
  Purchase #6 $145.86   9.352%   $159.5008   $159.50   $159.50   $159.50  
  Purchase #7 $137.70   5.502%   $145.2763   $145.28   $145.30   $145.30  
  7 purchase totals = $1,042.41       $1,141.7136   $1,141.72   $1,141.75   $1,141.80