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 $147.97   12.396%   $166.3124   $166.31   $166.30   $166.30  
  Purchase #2 $110.69   5.472%   $116.747   $116.75   $116.75   $116.70  
  Purchase #3 $22.98   6.414%   $24.4539   $24.45   $24.45   $24.50  
  Purchase #4 $193.27   10.604%   $213.7644   $213.76   $213.75   $213.80  
  Purchase #5 $192.76   12.735%   $217.308   $217.31   $217.30   $217.30  
  Purchase #6 $23.88   8.451%   $25.8981   $25.90   $25.90   $25.90  
  Purchase #7 $90.82   7.331%   $97.478   $97.48   $97.50   $97.50  
  7 purchase totals = $782.37       $861.9618   $861.96   $861.95   $862.00