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 $227.33   9.378%   $248.649   $248.65   $248.65   $248.60  
  Purchase #2 $94.63   3.141%   $97.6023   $97.60   $97.60   $97.60  
  Purchase #3 $66.67   6.643%   $71.0989   $71.10   $71.10   $71.10  
  Purchase #4 $88.56   9.150%   $96.6632   $96.66   $96.65   $96.70  
  Purchase #5 $178.47   4.219%   $185.9996   $186.00   $186.00   $186.00  
  Purchase #6 $14.48   10.154%   $15.9503   $15.95   $15.95   $16.00  
  Purchase #7 $179.96   6.384%   $191.4486   $191.45   $191.45   $191.40  
  7 purchase totals = $850.10       $907.4119   $907.41   $907.40   $907.40