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 $214.84   6.857%   $229.5716   $229.57   $229.55   $229.60  
  Purchase #2 $96.93   3.847%   $100.6589   $100.66   $100.65   $100.70  
  Purchase #3 $167.38   3.538%   $173.3019   $173.30   $173.30   $173.30  
  Purchase #4 $65.68   4.645%   $68.7308   $68.73   $68.75   $68.70  
  Purchase #5 $164.96   13.417%   $187.0927   $187.09   $187.10   $187.10  
  Purchase #6 $151.83   13.489%   $172.3103   $172.31   $172.30   $172.30  
  Purchase #7 $73.34   7.709%   $78.9938   $78.99   $79.00   $79.00  
  7 purchase totals = $934.96       $1,010.6600   $1,010.65   $1,010.65   $1,010.70