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 $246.45   10.769%   $272.9902   $272.99   $273.00   $273.00  
  Purchase #2 $59.56   10.643%   $65.899   $65.90   $65.90   $65.90  
  Purchase #3 $224.66   5.374%   $236.7332   $236.73   $236.75   $236.70  
  Purchase #4 $87.80   5.443%   $92.579   $92.58   $92.60   $92.60  
  Purchase #5 $84.33   5.105%   $88.635   $88.64   $88.65   $88.60  
  Purchase #6 $167.57   12.312%   $188.2012   $188.20   $188.20   $188.20  
  Purchase #7 $195.33   4.406%   $203.9362   $203.94   $203.95   $203.90  
  7 purchase totals = $1,065.70       $1,148.9738   $1,148.98   $1,149.05   $1,148.90