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 $112.64   12.113%   $126.2841   $126.28   $126.30   $126.30  
  Purchase #2 $228.60   4.404%   $238.6675   $238.67   $238.65   $238.70  
  Purchase #3 $169.88   8.555%   $184.4132   $184.41   $184.40   $184.40  
  Purchase #4 $12.25   13.732%   $13.9322   $13.93   $13.95   $13.90  
  Purchase #5 $241.99   10.464%   $267.3118   $267.31   $267.30   $267.30  
  Purchase #6 $140.87   7.144%   $150.9338   $150.93   $150.95   $150.90  
  Purchase #7 $59.33   5.512%   $62.6003   $62.60   $62.60   $62.60  
  7 purchase totals = $965.56       $1,044.1429   $1,044.13   $1,044.15   $1,044.10