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 $154.57   8.672%   $167.9743   $167.97   $167.95   $168.00  
  Purchase #2 $249.81   6.208%   $265.3182   $265.32   $265.30   $265.30  
  Purchase #3 $118.67   11.808%   $132.6826   $132.68   $132.70   $132.70  
  Purchase #4 $89.32   10.802%   $98.9683   $98.97   $98.95   $99.00  
  Purchase #5 $248.36   4.671%   $259.9609   $259.96   $259.95   $260.00  
  Purchase #6 $47.86   3.154%   $49.3695   $49.37   $49.35   $49.40  
  Purchase #7 $230.50   6.423%   $245.305   $245.31   $245.30   $245.30  
  7 purchase totals = $1,139.09       $1,219.5788   $1,219.58   $1,219.50   $1,219.70