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 $61.30   5.565%   $64.7113   $64.71   $64.70   $64.70  
  Purchase #2 $188.74   8.485%   $204.7546   $204.75   $204.75   $204.80  
  Purchase #3 $60.58   5.200%   $63.7302   $63.73   $63.75   $63.70  
  Purchase #4 $204.82   9.838%   $224.9702   $224.97   $224.95   $225.00  
  Purchase #5 $135.96   7.613%   $146.3106   $146.31   $146.30   $146.30  
  Purchase #6 $61.38   11.211%   $68.2613   $68.26   $68.25   $68.30  
  Purchase #7 $242.54   3.633%   $251.3515   $251.35   $251.35   $251.40  
  7 purchase totals = $955.32       $1,024.0897   $1,024.08   $1,024.05   $1,024.20