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 $56.59   12.224%   $63.5076   $63.51   $63.50   $63.50  
  Purchase #2 $247.25   10.643%   $273.5648   $273.56   $273.55   $273.60  
  Purchase #3 $231.50   6.294%   $246.0706   $246.07   $246.05   $246.10  
  Purchase #4 $159.40   5.811%   $168.6627   $168.66   $168.65   $168.70  
  Purchase #5 $137.96   11.615%   $153.9841   $153.98   $154.00   $154.00  
  Purchase #6 $204.76   13.177%   $231.7412   $231.74   $231.75   $231.70  
  Purchase #7 $126.81   7.494%   $136.3131   $136.31   $136.30   $136.30  
  7 purchase totals = $1,164.27       $1,273.8441   $1,273.83   $1,273.80   $1,273.90