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 $246.25   8.812%   $267.9496   $267.95   $267.95   $267.90  
  Purchase #2 $233.54   11.305%   $259.9417   $259.94   $259.95   $259.90  
  Purchase #3 $16.75   3.302%   $17.3031   $17.30   $17.30   $17.30  
  Purchase #4 $225.95   9.832%   $248.1654   $248.17   $248.15   $248.20  
  Purchase #5 $96.32   10.207%   $106.1514   $106.15   $106.15   $106.20  
  Purchase #6 $162.47   10.317%   $179.232   $179.23   $179.25   $179.20  
  Purchase #7 $189.64   8.774%   $206.279   $206.28   $206.30   $206.30  
  7 purchase totals = $1,170.92       $1,285.0222   $1,285.02   $1,285.05   $1,285.00