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 $94.58   3.386%   $97.7825   $97.78   $97.80   $97.80  
  Purchase #2 $244.78   6.758%   $261.3222   $261.32   $261.30   $261.30  
  Purchase #3 $87.36   12.571%   $98.342   $98.34   $98.35   $98.30  
  Purchase #4 $233.70   11.756%   $261.1738   $261.17   $261.15   $261.20  
  Purchase #5 $162.52   9.340%   $177.6994   $177.70   $177.70   $177.70  
  Purchase #6 $203.36   3.538%   $210.5549   $210.55   $210.55   $210.60  
  Purchase #7 $50.52   8.106%   $54.6152   $54.62   $54.60   $54.60  
  7 purchase totals = $1,076.82       $1,161.4900   $1,161.48   $1,161.45   $1,161.50