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 $221.97   6.114%   $235.5412   $235.54   $235.55   $235.50  
  Purchase #2 $24.58   4.310%   $25.6394   $25.64   $25.65   $25.60  
  Purchase #3 $125.85   5.668%   $132.9832   $132.98   $133.00   $133.00  
  Purchase #4 $208.78   8.829%   $227.2132   $227.21   $227.20   $227.20  
  Purchase #5 $110.37   6.302%   $117.3255   $117.33   $117.35   $117.30  
  Purchase #6 $150.26   7.223%   $161.1133   $161.11   $161.10   $161.10  
  Purchase #7 $250.68   5.733%   $265.0515   $265.05   $265.05   $265.10  
  7 purchase totals = $1,092.49       $1,164.8673   $1,164.86   $1,164.90   $1,164.80