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 $216.65   12.672%   $244.1039   $244.10   $244.10   $244.10  
  Purchase #2 $205.70   10.239%   $226.7616   $226.76   $226.75   $226.80  
  Purchase #3 $116.46   7.392%   $125.0687   $125.07   $125.05   $125.10  
  Purchase #4 $233.32   12.209%   $261.806   $261.81   $261.80   $261.80  
  Purchase #5 $84.68   6.656%   $90.3163   $90.32   $90.30   $90.30  
  Purchase #6 $46.38   5.344%   $48.8585   $48.86   $48.85   $48.90  
  Purchase #7 $244.59   5.344%   $257.6609   $257.66   $257.65   $257.70  
  7 purchase totals = $1,147.78       $1,254.5759   $1,254.58   $1,254.50   $1,254.70