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 $184.53   5.433%   $194.5555   $194.56   $194.55   $194.60  
  Purchase #2 $44.81   6.397%   $47.6765   $47.68   $47.70   $47.70  
  Purchase #3 $174.69   10.563%   $193.1425   $193.14   $193.15   $193.10  
  Purchase #4 $22.94   7.669%   $24.6993   $24.70   $24.70   $24.70  
  Purchase #5 $148.29   7.219%   $158.9951   $159.00   $159.00   $159.00  
  Purchase #6 $250.56   6.407%   $266.6134   $266.61   $266.60   $266.60  
  Purchase #7 $234.50   11.688%   $261.9084   $261.91   $261.90   $261.90  
  7 purchase totals = $1,060.32       $1,147.5907   $1,147.60   $1,147.60   $1,147.60