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 $203.84   3.602%   $211.1823   $211.18   $211.20   $211.20  
  Purchase #2 $180.35   3.482%   $186.6298   $186.63   $186.65   $186.60  
  Purchase #3 $219.76   4.627%   $229.9283   $229.93   $229.95   $229.90  
  Purchase #4 $144.53   4.554%   $151.1119   $151.11   $151.10   $151.10  
  Purchase #5 $248.38   11.162%   $276.1042   $276.10   $276.10   $276.10  
  Purchase #6 $8.36   3.554%   $8.6571   $8.66   $8.65   $8.70  
  Purchase #7 $169.84   3.825%   $176.3364   $176.34   $176.35   $176.30  
  7 purchase totals = $1,175.06       $1,239.9500   $1,239.95   $1,240.00   $1,239.90