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 $229.47   4.833%   $240.5603   $240.56   $240.55   $240.60  
  Purchase #2 $93.92   7.725%   $101.1753   $101.18   $101.20   $101.20  
  Purchase #3 $66.75   9.248%   $72.923   $72.92   $72.90   $72.90  
  Purchase #4 $40.79   6.543%   $43.4589   $43.46   $43.45   $43.50  
  Purchase #5 $64.85   8.575%   $70.4109   $70.41   $70.40   $70.40  
  Purchase #6 $206.73   4.764%   $216.5786   $216.58   $216.60   $216.60  
  Purchase #7 $248.55   11.270%   $276.5616   $276.56   $276.55   $276.60  
  7 purchase totals = $951.06       $1,021.6686   $1,021.67   $1,021.65   $1,021.80