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 $113.72   4.841%   $119.2252   $119.23   $119.25   $119.20  
  Purchase #2 $140.55   10.709%   $155.6015   $155.60   $155.60   $155.60  
  Purchase #3 $72.80   13.433%   $82.5792   $82.58   $82.60   $82.60  
  Purchase #4 $227.70   13.374%   $258.1526   $258.15   $258.15   $258.20  
  Purchase #5 $62.29   12.343%   $69.9785   $69.98   $70.00   $70.00  
  Purchase #6 $14.58   3.725%   $15.1231   $15.12   $15.10   $15.10  
  Purchase #7 $201.41   6.114%   $213.7242   $213.72   $213.70   $213.70  
  7 purchase totals = $833.05       $914.3843   $914.38   $914.40   $914.40