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 $23.33   5.562%   $24.6276   $24.63   $24.65   $24.60  
  Purchase #2 $47.79   10.147%   $52.6393   $52.64   $52.65   $52.60  
  Purchase #3 $58.33   6.772%   $62.2801   $62.28   $62.30   $62.30  
  Purchase #4 $202.62   9.258%   $221.3786   $221.38   $221.40   $221.40  
  Purchase #5 $148.71   8.411%   $161.218   $161.22   $161.20   $161.20  
  Purchase #6 $165.84   12.312%   $186.2582   $186.26   $186.25   $186.30  
  Purchase #7 $35.43   3.112%   $36.5326   $36.53   $36.55   $36.50  
  7 purchase totals = $682.05       $744.9344   $744.94   $745.00   $744.90