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 $36.92   13.563%   $41.9275   $41.93   $41.95   $41.90  
  Purchase #2 $154.87   4.389%   $161.6672   $161.67   $161.65   $161.70  
  Purchase #3 $126.89   10.826%   $140.6271   $140.63   $140.65   $140.60  
  Purchase #4 $201.61   10.637%   $223.0553   $223.06   $223.05   $223.10  
  Purchase #5 $49.86   5.207%   $52.4562   $52.46   $52.45   $52.50  
  Purchase #6 $99.84   9.511%   $109.3358   $109.34   $109.35   $109.30  
  Purchase #7 $151.49   11.700%   $169.2143   $169.21   $169.20   $169.20  
  7 purchase totals = $821.48       $898.2834   $898.30   $898.30   $898.30