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 $165.86   6.728%   $177.0191   $177.02   $177.00   $177.00  
  Purchase #2 $206.36   3.326%   $213.2235   $213.22   $213.20   $213.20  
  Purchase #3 $219.49   6.565%   $233.8995   $233.90   $233.90   $233.90  
  Purchase #4 $248.47   6.711%   $265.1448   $265.14   $265.15   $265.10  
  Purchase #5 $57.32   12.118%   $64.266   $64.27   $64.25   $64.30  
  Purchase #6 $178.82   3.601%   $185.2593   $185.26   $185.25   $185.30  
  Purchase #7 $83.58   6.189%   $88.7528   $88.75   $88.75   $88.80  
  7 purchase totals = $1,159.90       $1,227.5650   $1,227.56   $1,227.50   $1,227.60