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 $126.60   6.361%   $134.653   $134.65   $134.65   $134.70  
  Purchase #2 $72.59   6.849%   $77.5617   $77.56   $77.55   $77.60  
  Purchase #3 $148.41   13.130%   $167.8962   $167.90   $167.90   $167.90  
  Purchase #4 $177.79   11.801%   $198.771   $198.77   $198.75   $198.80  
  Purchase #5 $232.54   5.487%   $245.2995   $245.30   $245.30   $245.30  
  Purchase #6 $20.96   6.380%   $22.2972   $22.30   $22.30   $22.30  
  Purchase #7 $131.34   4.606%   $137.3895   $137.39   $137.40   $137.40  
  7 purchase totals = $910.23       $983.8681   $983.87   $983.85   $984.00