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 $58.65   10.373%   $64.7338   $64.73   $64.75   $64.70  
  Purchase #2 $114.98   7.488%   $123.5897   $123.59   $123.60   $123.60  
  Purchase #3 $200.50   7.194%   $214.924   $214.92   $214.90   $214.90  
  Purchase #4 $103.76   7.606%   $111.652   $111.65   $111.65   $111.70  
  Purchase #5 $245.66   5.109%   $258.2108   $258.21   $258.20   $258.20  
  Purchase #6 $129.75   4.169%   $135.1593   $135.16   $135.15   $135.20  
  Purchase #7 $5.97   4.529%   $6.2404   $6.24   $6.25   $6.20  
  7 purchase totals = $859.27       $914.5100   $914.50   $914.50   $914.50