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 $177.63   13.490%   $201.5923   $201.59   $201.60   $201.60  
  Purchase #2 $112.57   4.734%   $117.8991   $117.90   $117.90   $117.90  
  Purchase #3 $204.82   9.741%   $224.7715   $224.77   $224.75   $224.80  
  Purchase #4 $98.82   11.526%   $110.21   $110.21   $110.20   $110.20  
  Purchase #5 $232.92   12.854%   $262.8595   $262.86   $262.85   $262.90  
  Purchase #6 $119.53   10.667%   $132.2803   $132.28   $132.30   $132.30  
  Purchase #7 $131.49   13.186%   $148.8283   $148.83   $148.85   $148.80  
  7 purchase totals = $1,077.78       $1,198.4410   $1,198.44   $1,198.45   $1,198.50