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 $93.85   4.576%   $98.1446   $98.14   $98.15   $98.10  
  Purchase #2 $89.89   4.616%   $94.0393   $94.04   $94.05   $94.00  
  Purchase #3 $59.37   11.582%   $66.2462   $66.25   $66.25   $66.20  
  Purchase #4 $171.58   12.168%   $192.4579   $192.46   $192.45   $192.50  
  Purchase #5 $39.67   7.782%   $42.7571   $42.76   $42.75   $42.80  
  Purchase #6 $237.74   11.550%   $265.199   $265.20   $265.20   $265.20  
  Purchase #7 $34.96   4.501%   $36.5335   $36.53   $36.55   $36.50  
  7 purchase totals = $727.06       $795.3776   $795.38   $795.40   $795.30