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 $217.64   13.503%   $247.0279   $247.03   $247.05   $247.00  
  Purchase #2 $231.27   8.249%   $250.3475   $250.35   $250.35   $250.30  
  Purchase #3 $38.29   8.659%   $41.6055   $41.61   $41.60   $41.60  
  Purchase #4 $201.66   6.769%   $215.3104   $215.31   $215.30   $215.30  
  Purchase #5 $125.43   8.103%   $135.5936   $135.59   $135.60   $135.60  
  Purchase #6 $244.44   9.248%   $267.0458   $267.05   $267.05   $267.00  
  Purchase #7 $69.35   7.570%   $74.5998   $74.60   $74.60   $74.60  
  7 purchase totals = $1,128.08       $1,231.5305   $1,231.54   $1,231.55   $1,231.40