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 $67.73   12.271%   $76.0411   $76.04   $76.05   $76.00  
  Purchase #2 $169.95   12.403%   $191.0289   $191.03   $191.05   $191.00  
  Purchase #3 $13.82   4.147%   $14.3931   $14.39   $14.40   $14.40  
  Purchase #4 $202.55   9.340%   $221.4682   $221.47   $221.45   $221.50  
  Purchase #5 $204.30   11.574%   $227.9457   $227.95   $227.95   $227.90  
  Purchase #6 $91.99   5.110%   $96.6907   $96.69   $96.70   $96.70  
  Purchase #7 $226.67   9.376%   $247.9226   $247.92   $247.90   $247.90  
  7 purchase totals = $977.01       $1,075.4903   $1,075.49   $1,075.50   $1,075.40