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 $159.45   13.781%   $181.4238   $181.42   $181.40   $181.40  
  Purchase #2 $194.65   5.117%   $204.6102   $204.61   $204.60   $204.60  
  Purchase #3 $121.29   3.493%   $125.5267   $125.53   $125.55   $125.50  
  Purchase #4 $142.97   5.677%   $151.0864   $151.09   $151.10   $151.10  
  Purchase #5 $57.82   4.389%   $60.3577   $60.36   $60.35   $60.40  
  Purchase #6 $229.89   8.574%   $249.6008   $249.60   $249.60   $249.60  
  Purchase #7 $203.47   8.818%   $221.412   $221.41   $221.40   $221.40  
  7 purchase totals = $1,109.54       $1,194.0176   $1,194.02   $1,194.00   $1,194.00