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 $233.87   12.707%   $263.5879   $263.59   $263.60   $263.60  
  Purchase #2 $212.55   7.668%   $228.8483   $228.85   $228.85   $228.80  
  Purchase #3 $174.74   3.296%   $180.4994   $180.50   $180.50   $180.50  
  Purchase #4 $246.33   3.614%   $255.2324   $255.23   $255.25   $255.20  
  Purchase #5 $175.32   11.678%   $195.7939   $195.79   $195.80   $195.80  
  Purchase #6 $236.63   5.333%   $249.2495   $249.25   $249.25   $249.20  
  Purchase #7 $237.45   5.579%   $250.6973   $250.70   $250.70   $250.70  
  7 purchase totals = $1,516.89       $1,623.9087   $1,623.91   $1,623.95   $1,623.80