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 $206.42   4.161%   $215.0091   $215.01   $215.00   $215.00  
  Purchase #2 $84.71   3.634%   $87.7884   $87.79   $87.80   $87.80  
  Purchase #3 $171.35   6.583%   $182.63   $182.63   $182.65   $182.60  
  Purchase #4 $247.48   3.852%   $257.0129   $257.01   $257.00   $257.00  
  Purchase #5 $220.84   6.204%   $234.5409   $234.54   $234.55   $234.50  
  Purchase #6 $53.54   8.280%   $57.9731   $57.97   $57.95   $58.00  
  Purchase #7 $120.48   10.124%   $132.6774   $132.68   $132.70   $132.70  
  7 purchase totals = $1,104.82       $1,167.6318   $1,167.63   $1,167.65   $1,167.60