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 $62.42   10.572%   $69.019   $69.02   $69.00   $69.00  
  Purchase #2 $19.75   4.254%   $20.5902   $20.59   $20.60   $20.60  
  Purchase #3 $81.30   4.212%   $84.7244   $84.72   $84.70   $84.70  
  Purchase #4 $111.62   7.169%   $119.622   $119.62   $119.60   $119.60  
  Purchase #5 $78.60   13.185%   $88.9634   $88.96   $88.95   $89.00  
  Purchase #6 $240.93   6.671%   $257.0024   $257.00   $257.00   $257.00  
  Purchase #7 $224.87   10.262%   $247.9462   $247.95   $247.95   $247.90  
  7 purchase totals = $819.49       $887.8676   $887.86   $887.80   $887.80