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 $84.79   11.628%   $94.6494   $94.65   $94.65   $94.60  
  Purchase #2 $213.62   9.701%   $234.3433   $234.34   $234.35   $234.30  
  Purchase #3 $93.25   13.201%   $105.5599   $105.56   $105.55   $105.60  
  Purchase #4 $56.26   9.689%   $61.711   $61.71   $61.70   $61.70  
  Purchase #5 $248.56   10.419%   $274.4575   $274.46   $274.45   $274.50  
  Purchase #6 $177.79   8.728%   $193.3075   $193.31   $193.30   $193.30  
  Purchase #7 $7.99   9.742%   $8.7684   $8.77   $8.75   $8.80  
  7 purchase totals = $882.26       $972.7970   $972.80   $972.75   $972.80