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 $178.87   10.639%   $197.9   $197.90   $197.90   $197.90  
  Purchase #2 $77.34   9.107%   $84.3834   $84.38   $84.40   $84.40  
  Purchase #3 $141.28   12.851%   $159.4359   $159.44   $159.45   $159.40  
  Purchase #4 $241.78   4.715%   $253.1799   $253.18   $253.20   $253.20  
  Purchase #5 $62.31   11.390%   $69.4071   $69.41   $69.40   $69.40  
  Purchase #6 $26.84   12.444%   $30.18   $30.18   $30.20   $30.20  
  Purchase #7 $9.55   6.774%   $10.1969   $10.20   $10.20   $10.20  
  7 purchase totals = $737.97       $804.6832   $804.69   $804.75   $804.70