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 $243.90   10.526%   $269.5729   $269.57   $269.55   $269.60  
  Purchase #2 $18.64   4.867%   $19.5472   $19.55   $19.55   $19.50  
  Purchase #3 $146.55   7.390%   $157.38   $157.38   $157.40   $157.40  
  Purchase #4 $128.44   12.624%   $144.6543   $144.65   $144.65   $144.70  
  Purchase #5 $193.40   6.630%   $206.2224   $206.22   $206.20   $206.20  
  Purchase #6 $124.39   11.600%   $138.8192   $138.82   $138.80   $138.80  
  Purchase #7 $75.95   3.206%   $78.385   $78.39   $78.40   $78.40  
  7 purchase totals = $931.27       $1,014.5810   $1,014.58   $1,014.55   $1,014.60