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 $79.29   4.393%   $82.7732   $82.77   $82.75   $82.80  
  Purchase #2 $106.63   8.496%   $115.6893   $115.69   $115.70   $115.70  
  Purchase #3 $213.88   9.183%   $233.5206   $233.52   $233.50   $233.50  
  Purchase #4 $94.61   3.485%   $97.9072   $97.91   $97.90   $97.90  
  Purchase #5 $205.26   6.413%   $218.4233   $218.42   $218.40   $218.40  
  Purchase #6 $244.65   6.688%   $261.0122   $261.01   $261.00   $261.00  
  Purchase #7 $62.34   6.332%   $66.2874   $66.29   $66.30   $66.30  
  7 purchase totals = $1,006.66       $1,075.6132   $1,075.61   $1,075.55   $1,075.60