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 $57.96   10.153%   $63.8447   $63.84   $63.85   $63.80  
  Purchase #2 $222.89   11.223%   $247.9049   $247.90   $247.90   $247.90  
  Purchase #3 $199.97   10.362%   $220.6909   $220.69   $220.70   $220.70  
  Purchase #4 $207.91   9.585%   $227.8382   $227.84   $227.85   $227.80  
  Purchase #5 $63.82   11.664%   $71.264   $71.26   $71.25   $71.30  
  Purchase #6 $108.70   4.612%   $113.7132   $113.71   $113.70   $113.70  
  Purchase #7 $219.69   10.138%   $241.9622   $241.96   $241.95   $242.00  
  7 purchase totals = $1,080.94       $1,187.2181   $1,187.20   $1,187.20   $1,187.20