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 $115.76   5.614%   $122.2588   $122.26   $122.25   $122.30  
  Purchase #2 $95.35   3.457%   $98.6462   $98.65   $98.65   $98.60  
  Purchase #3 $22.30   11.260%   $24.811   $24.81   $24.80   $24.80  
  Purchase #4 $144.40   4.751%   $151.2604   $151.26   $151.25   $151.30  
  Purchase #5 $201.98   10.872%   $223.9393   $223.94   $223.95   $223.90  
  Purchase #6 $139.28   10.222%   $153.5172   $153.52   $153.50   $153.50  
  Purchase #7 $164.26   8.776%   $178.6755   $178.68   $178.70   $178.70  
  7 purchase totals = $883.33       $953.1084   $953.12   $953.10   $953.10