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 $75.59   12.667%   $85.165   $85.17   $85.15   $85.20  
  Purchase #2 $239.97   3.486%   $248.3354   $248.34   $248.35   $248.30  
  Purchase #3 $157.88   3.515%   $163.4295   $163.43   $163.45   $163.40  
  Purchase #4 $249.54   13.195%   $282.4668   $282.47   $282.45   $282.50  
  Purchase #5 $231.89   10.838%   $257.0222   $257.02   $257.00   $257.00  
  Purchase #6 $133.48   12.714%   $150.4506   $150.45   $150.45   $150.50  
  Purchase #7 $24.53   11.810%   $27.427   $27.43   $27.45   $27.40  
  7 purchase totals = $1,112.88       $1,214.2965   $1,214.31   $1,214.30   $1,214.30