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 $224.66   8.604%   $243.9897   $243.99   $244.00   $244.00  
  Purchase #2 $97.98   3.150%   $101.0664   $101.07   $101.05   $101.10  
  Purchase #3 $91.84   6.293%   $97.6195   $97.62   $97.60   $97.60  
  Purchase #4 $230.33   8.277%   $249.3944   $249.39   $249.40   $249.40  
  Purchase #5 $15.27   5.246%   $16.0711   $16.07   $16.05   $16.10  
  Purchase #6 $55.33   8.640%   $60.1105   $60.11   $60.10   $60.10  
  Purchase #7 $157.48   7.811%   $169.7808   $169.78   $169.80   $169.80  
  7 purchase totals = $872.89       $938.0324   $938.03   $938.00   $938.10