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 $243.85   6.355%   $259.3467   $259.35   $259.35   $259.30  
  Purchase #2 $127.51   11.136%   $141.7095   $141.71   $141.70   $141.70  
  Purchase #3 $234.67   8.289%   $254.1218   $254.12   $254.10   $254.10  
  Purchase #4 $242.33   9.165%   $264.5395   $264.54   $264.55   $264.50  
  Purchase #5 $108.46   8.512%   $117.6921   $117.69   $117.70   $117.70  
  Purchase #6 $158.46   5.293%   $166.8473   $166.85   $166.85   $166.80  
  Purchase #7 $110.95   7.834%   $119.6418   $119.64   $119.65   $119.60  
  7 purchase totals = $1,226.23       $1,323.8987   $1,323.90   $1,323.90   $1,323.70