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 $94.82   6.732%   $101.2033   $101.20   $101.20   $101.20  
  Purchase #2 $67.53   13.401%   $76.5797   $76.58   $76.60   $76.60  
  Purchase #3 $225.71   12.368%   $253.6258   $253.63   $253.65   $253.60  
  Purchase #4 $190.26   11.245%   $211.6547   $211.65   $211.65   $211.70  
  Purchase #5 $144.49   8.200%   $156.3382   $156.34   $156.35   $156.30  
  Purchase #6 $211.64   4.490%   $221.1426   $221.14   $221.15   $221.10  
  Purchase #7 $222.30   7.650%   $239.306   $239.31   $239.30   $239.30  
  7 purchase totals = $1,156.75       $1,259.8503   $1,259.85   $1,259.90   $1,259.80