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 $53.76   13.536%   $61.037   $61.04   $61.05   $61.00  
  Purchase #2 $185.64   8.194%   $200.8513   $200.85   $200.85   $200.90  
  Purchase #3 $62.70   5.653%   $66.2444   $66.24   $66.25   $66.20  
  Purchase #4 $197.66   8.155%   $213.7792   $213.78   $213.80   $213.80  
  Purchase #5 $117.45   13.207%   $132.9616   $132.96   $132.95   $133.00  
  Purchase #6 $66.67   11.194%   $74.133   $74.13   $74.15   $74.10  
  Purchase #7 $118.30   5.162%   $124.4066   $124.41   $124.40   $124.40  
  7 purchase totals = $802.18       $873.4131   $873.41   $873.45   $873.40