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 $207.76   12.748%   $234.2452   $234.25   $234.25   $234.20  
  Purchase #2 $101.87   11.617%   $113.7042   $113.70   $113.70   $113.70  
  Purchase #3 $121.76   9.439%   $133.2529   $133.25   $133.25   $133.30  
  Purchase #4 $210.91   4.228%   $219.8273   $219.83   $219.85   $219.80  
  Purchase #5 $164.91   8.437%   $178.8235   $178.82   $178.80   $178.80  
  Purchase #6 $241.54   13.633%   $274.4691   $274.47   $274.45   $274.50  
  Purchase #7 $107.69   7.287%   $115.5374   $115.54   $115.55   $115.50  
  7 purchase totals = $1,156.44       $1,269.8596   $1,269.86   $1,269.85   $1,269.80