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 $56.47   12.195%   $63.3565   $63.36   $63.35   $63.40  
  Purchase #2 $206.58   9.642%   $226.4984   $226.50   $226.50   $226.50  
  Purchase #3 $190.99   4.478%   $199.5425   $199.54   $199.55   $199.50  
  Purchase #4 $60.82   13.726%   $69.1682   $69.17   $69.15   $69.20  
  Purchase #5 $118.35   6.403%   $125.928   $125.93   $125.95   $125.90  
  Purchase #6 $200.74   4.247%   $209.2654   $209.27   $209.25   $209.30  
  Purchase #7 $212.63   12.410%   $239.0174   $239.02   $239.00   $239.00  
  7 purchase totals = $1,046.58       $1,132.7764   $1,132.79   $1,132.75   $1,132.80