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 $57.55   4.772%   $60.2963   $60.30   $60.30   $60.30  
  Purchase #2 $232.28   6.342%   $247.0112   $247.01   $247.00   $247.00  
  Purchase #3 $175.56   11.815%   $196.3024   $196.30   $196.30   $196.30  
  Purchase #4 $248.49   3.368%   $256.8591   $256.86   $256.85   $256.90  
  Purchase #5 $82.35   5.485%   $86.8669   $86.87   $86.85   $86.90  
  Purchase #6 $137.41   9.727%   $150.7759   $150.78   $150.80   $150.80  
  Purchase #7 $231.56   9.177%   $252.8103   $252.81   $252.80   $252.80  
  7 purchase totals = $1,165.20       $1,250.9221   $1,250.93   $1,250.90   $1,251.00