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 $22.58   11.847%   $25.2551   $25.26   $25.25   $25.30  
  Purchase #2 $62.93   5.701%   $66.5176   $66.52   $66.50   $66.50  
  Purchase #3 $36.35   7.130%   $38.9418   $38.94   $38.95   $38.90  
  Purchase #4 $190.73   8.464%   $206.8734   $206.87   $206.85   $206.90  
  Purchase #5 $165.48   10.734%   $183.2426   $183.24   $183.25   $183.20  
  Purchase #6 $39.34   5.773%   $41.6111   $41.61   $41.60   $41.60  
  Purchase #7 $171.84   5.105%   $180.6124   $180.61   $180.60   $180.60  
  7 purchase totals = $689.25       $743.0540   $743.05   $743.00   $743.00