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 $61.27   13.545%   $69.569   $69.57   $69.55   $69.60  
  Purchase #2 $246.37   11.434%   $274.5399   $274.54   $274.55   $274.50  
  Purchase #3 $221.55   8.282%   $239.8988   $239.90   $239.90   $239.90  
  Purchase #4 $56.96   8.623%   $61.8717   $61.87   $61.85   $61.90  
  Purchase #5 $144.48   13.527%   $164.0238   $164.02   $164.00   $164.00  
  Purchase #6 $63.36   6.778%   $67.6545   $67.65   $67.65   $67.70  
  Purchase #7 $115.46   3.336%   $119.3117   $119.31   $119.30   $119.30  
  7 purchase totals = $909.45       $996.8694   $996.86   $996.80   $996.90