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 $101.25   13.871%   $115.2944   $115.29   $115.30   $115.30  
  Purchase #2 $74.87   10.270%   $82.5591   $82.56   $82.55   $82.60  
  Purchase #3 $146.99   7.181%   $157.5454   $157.55   $157.55   $157.50  
  Purchase #4 $154.42   7.823%   $166.5003   $166.50   $166.50   $166.50  
  Purchase #5 $201.68   12.473%   $226.8355   $226.84   $226.85   $226.80  
  Purchase #6 $201.69   9.221%   $220.2878   $220.29   $220.30   $220.30  
  Purchase #7 $156.34   7.848%   $168.6096   $168.61   $168.60   $168.60  
  7 purchase totals = $1,037.24       $1,137.6321   $1,137.64   $1,137.65   $1,137.60