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 $49.51   13.228%   $56.0592   $56.06   $56.05   $56.10  
  Purchase #2 $134.82   12.675%   $151.9084   $151.91   $151.90   $151.90  
  Purchase #3 $119.66   13.306%   $135.582   $135.58   $135.60   $135.60  
  Purchase #4 $85.67   6.537%   $91.2702   $91.27   $91.25   $91.30  
  Purchase #5 $22.73   8.768%   $24.723   $24.72   $24.70   $24.70  
  Purchase #6 $118.88   10.823%   $131.7464   $131.75   $131.75   $131.70  
  Purchase #7 $134.72   9.838%   $147.9738   $147.97   $147.95   $148.00  
  7 purchase totals = $665.99       $739.2630   $739.26   $739.20   $739.30