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 $61.87   8.230%   $66.9619   $66.96   $66.95   $67.00  
  Purchase #2 $203.38   3.212%   $209.9126   $209.91   $209.90   $209.90  
  Purchase #3 $231.91   13.296%   $262.7448   $262.74   $262.75   $262.70  
  Purchase #4 $128.50   5.277%   $135.2809   $135.28   $135.30   $135.30  
  Purchase #5 $170.54   10.200%   $187.9351   $187.94   $187.95   $187.90  
  Purchase #6 $178.77   10.814%   $198.1022   $198.10   $198.10   $198.10  
  Purchase #7 $177.72   10.154%   $195.7657   $195.77   $195.75   $195.80  
  7 purchase totals = $1,152.69       $1,256.7032   $1,256.70   $1,256.70   $1,256.70