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 $180.54   11.328%   $200.9916   $200.99   $201.00   $201.00  
  Purchase #2 $88.30   9.451%   $96.6452   $96.65   $96.65   $96.60  
  Purchase #3 $69.61   12.145%   $78.0641   $78.06   $78.05   $78.10  
  Purchase #4 $184.85   5.480%   $194.9798   $194.98   $195.00   $195.00  
  Purchase #5 $223.57   9.566%   $244.9567   $244.96   $244.95   $245.00  
  Purchase #6 $93.87   7.870%   $101.2576   $101.26   $101.25   $101.30  
  Purchase #7 $101.35   3.446%   $104.8425   $104.84   $104.85   $104.80  
  7 purchase totals = $942.09       $1,021.7375   $1,021.74   $1,021.75   $1,021.80