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 $65.90   10.680%   $72.9381   $72.94   $72.95   $72.90  
  Purchase #2 $197.51   11.664%   $220.5476   $220.55   $220.55   $220.50  
  Purchase #3 $24.81   4.263%   $25.8677   $25.87   $25.85   $25.90  
  Purchase #4 $115.63   11.614%   $129.0593   $129.06   $129.05   $129.10  
  Purchase #5 $92.53   5.433%   $97.5572   $97.56   $97.55   $97.60  
  Purchase #6 $175.87   9.294%   $192.2154   $192.22   $192.20   $192.20  
  Purchase #7 $80.78   5.516%   $85.2358   $85.24   $85.25   $85.20  
  7 purchase totals = $753.03       $823.4211   $823.44   $823.40   $823.40