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 $219.69   10.873%   $243.5769   $243.58   $243.60   $243.60  
  Purchase #2 $174.31   4.351%   $181.8942   $181.89   $181.90   $181.90  
  Purchase #3 $137.92   11.253%   $153.4401   $153.44   $153.45   $153.40  
  Purchase #4 $242.91   12.636%   $273.6041   $273.60   $273.60   $273.60  
  Purchase #5 $132.55   11.103%   $147.267   $147.27   $147.25   $147.30  
  Purchase #6 $118.76   5.454%   $125.2372   $125.24   $125.25   $125.20  
  Purchase #7 $156.95   3.341%   $162.1937   $162.19   $162.20   $162.20  
  7 purchase totals = $1,183.09       $1,287.2132   $1,287.21   $1,287.25   $1,287.20