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 $21.89   10.671%   $24.2259   $24.23   $24.25   $24.20  
  Purchase #2 $145.69   5.479%   $153.6724   $153.67   $153.65   $153.70  
  Purchase #3 $125.30   7.250%   $134.3843   $134.38   $134.40   $134.40  
  Purchase #4 $244.39   13.509%   $277.4046   $277.40   $277.40   $277.40  
  Purchase #5 $93.29   3.345%   $96.4106   $96.41   $96.40   $96.40  
  Purchase #6 $198.96   6.195%   $211.2856   $211.29   $211.30   $211.30  
  Purchase #7 $48.82   13.692%   $55.5044   $55.50   $55.50   $55.50  
  7 purchase totals = $878.34       $952.8878   $952.88   $952.90   $952.90