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 $248.59   6.265%   $264.1642   $264.16   $264.15   $264.20  
  Purchase #2 $83.44   11.219%   $92.8011   $92.80   $92.80   $92.80  
  Purchase #3 $115.45   11.793%   $129.065   $129.07   $129.05   $129.10  
  Purchase #4 $203.27   13.236%   $230.1748   $230.17   $230.15   $230.20  
  Purchase #5 $187.73   12.319%   $210.8565   $210.86   $210.85   $210.90  
  Purchase #6 $196.59   6.784%   $209.9267   $209.93   $209.95   $209.90  
  Purchase #7 $60.97   12.466%   $68.5705   $68.57   $68.55   $68.60  
  7 purchase totals = $1,096.04       $1,205.5588   $1,205.56   $1,205.50   $1,205.70