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 $25.96   3.425%   $26.8491   $26.85   $26.85   $26.80  
  Purchase #2 $220.26   11.215%   $244.9622   $244.96   $244.95   $245.00  
  Purchase #3 $133.71   13.512%   $151.7769   $151.78   $151.80   $151.80  
  Purchase #4 $88.26   6.698%   $94.1717   $94.17   $94.15   $94.20  
  Purchase #5 $138.39   10.819%   $153.3624   $153.36   $153.35   $153.40  
  Purchase #6 $247.84   10.680%   $274.3093   $274.31   $274.30   $274.30  
  Purchase #7 $47.51   4.471%   $49.6342   $49.63   $49.65   $49.60  
  7 purchase totals = $901.93       $995.0658   $995.06   $995.05   $995.10