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 $231.38   6.334%   $246.0356   $246.04   $246.05   $246.00  
  Purchase #2 $58.42   11.686%   $65.247   $65.25   $65.25   $65.20  
  Purchase #3 $118.34   9.520%   $129.606   $129.61   $129.60   $129.60  
  Purchase #4 $165.69   13.708%   $188.4028   $188.40   $188.40   $188.40  
  Purchase #5 $199.96   7.461%   $214.879   $214.88   $214.90   $214.90  
  Purchase #6 $200.64   8.487%   $217.6683   $217.67   $217.65   $217.70  
  Purchase #7 $210.98   4.706%   $220.9087   $220.91   $220.90   $220.90  
  7 purchase totals = $1,185.41       $1,282.7474   $1,282.76   $1,282.75   $1,282.70