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 $220.34   9.661%   $241.627   $241.63   $241.65   $241.60  
  Purchase #2 $62.48   6.749%   $66.6968   $66.70   $66.70   $66.70  
  Purchase #3 $67.95   7.196%   $72.8397   $72.84   $72.85   $72.80  
  Purchase #4 $206.50   8.423%   $223.8935   $223.89   $223.90   $223.90  
  Purchase #5 $113.35   3.275%   $117.0622   $117.06   $117.05   $117.10  
  Purchase #6 $14.44   10.702%   $15.9854   $15.99   $16.00   $16.00  
  Purchase #7 $163.40   6.411%   $173.8756   $173.88   $173.90   $173.90  
  7 purchase totals = $848.46       $911.9802   $911.99   $912.05   $912.00