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 $60.28   11.156%   $67.0048   $67.00   $67.00   $67.00  
  Purchase #2 $130.34   7.527%   $140.1507   $140.15   $140.15   $140.20  
  Purchase #3 $166.87   3.732%   $173.0976   $173.10   $173.10   $173.10  
  Purchase #4 $17.42   6.793%   $18.6033   $18.60   $18.60   $18.60  
  Purchase #5 $214.74   10.806%   $237.9448   $237.94   $237.95   $237.90  
  Purchase #6 $88.29   4.337%   $92.1191   $92.12   $92.10   $92.10  
  Purchase #7 $87.85   11.719%   $98.1451   $98.15   $98.15   $98.10  
  7 purchase totals = $765.79       $827.0654   $827.06   $827.05   $827.00