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 $209.36   5.323%   $220.5042   $220.50   $220.50   $220.50  
  Purchase #2 $41.33   8.288%   $44.7554   $44.76   $44.75   $44.80  
  Purchase #3 $38.55   9.690%   $42.2855   $42.29   $42.30   $42.30  
  Purchase #4 $35.56   13.446%   $40.3414   $40.34   $40.35   $40.30  
  Purchase #5 $223.74   6.702%   $238.7351   $238.74   $238.75   $238.70  
  Purchase #6 $239.57   7.303%   $257.0658   $257.07   $257.05   $257.10  
  Purchase #7 $62.44   3.733%   $64.7709   $64.77   $64.75   $64.80  
  7 purchase totals = $850.55       $908.4583   $908.47   $908.45   $908.50