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 $57.66   9.197%   $62.963   $62.96   $62.95   $63.00  
  Purchase #2 $210.77   6.277%   $224   $224.00   $224.00   $224.00  
  Purchase #3 $239.97   6.253%   $254.9753   $254.98   $255.00   $255.00  
  Purchase #4 $110.67   4.836%   $116.022   $116.02   $116.00   $116.00  
  Purchase #5 $152.72   9.348%   $166.9963   $167.00   $167.00   $167.00  
  Purchase #6 $11.48   11.252%   $12.7717   $12.77   $12.75   $12.80  
  Purchase #7 $7.36   10.852%   $8.1587   $8.16   $8.15   $8.20  
  7 purchase totals = $790.63       $845.8870   $845.89   $845.85   $846.00