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 $191.68   3.262%   $197.9326   $197.93   $197.95   $197.90  
  Purchase #2 $76.32   8.149%   $82.5393   $82.54   $82.55   $82.50  
  Purchase #3 $250.50   4.873%   $262.7069   $262.71   $262.70   $262.70  
  Purchase #4 $219.25   6.183%   $232.8062   $232.81   $232.80   $232.80  
  Purchase #5 $205.76   6.625%   $219.3916   $219.39   $219.40   $219.40  
  Purchase #6 $32.76   11.526%   $36.5359   $36.54   $36.55   $36.50  
  Purchase #7 $205.72   9.232%   $224.7121   $224.71   $224.70   $224.70  
  7 purchase totals = $1,181.99       $1,256.6246   $1,256.63   $1,256.65   $1,256.50