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 $244.77   6.849%   $261.5343   $261.53   $261.55   $261.50  
  Purchase #2 $191.62   7.845%   $206.6526   $206.65   $206.65   $206.70  
  Purchase #3 $213.36   13.667%   $242.5199   $242.52   $242.50   $242.50  
  Purchase #4 $97.91   10.700%   $108.3864   $108.39   $108.40   $108.40  
  Purchase #5 $24.34   12.723%   $27.4368   $27.44   $27.45   $27.40  
  Purchase #6 $115.46   3.367%   $119.3475   $119.35   $119.35   $119.30  
  Purchase #7 $45.61   13.501%   $51.7678   $51.77   $51.75   $51.80  
  7 purchase totals = $933.07       $1,017.6453   $1,017.65   $1,017.65   $1,017.60