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 $87.76   7.799%   $94.6044   $94.60   $94.60   $94.60  
  Purchase #2 $225.99   13.497%   $256.4919   $256.49   $256.50   $256.50  
  Purchase #3 $204.60   8.263%   $221.5061   $221.51   $221.50   $221.50  
  Purchase #4 $90.66   8.624%   $98.4785   $98.48   $98.50   $98.50  
  Purchase #5 $191.60   7.158%   $205.3147   $205.31   $205.30   $205.30  
  Purchase #6 $131.67   4.600%   $137.7268   $137.73   $137.75   $137.70  
  Purchase #7 $132.64   12.122%   $148.7186   $148.72   $148.70   $148.70  
  7 purchase totals = $1,064.92       $1,162.8410   $1,162.84   $1,162.85   $1,162.80