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 $23.62   12.569%   $26.5888   $26.59   $26.60   $26.60  
  Purchase #2 $165.83   10.360%   $183.01   $183.01   $183.00   $183.00  
  Purchase #3 $115.80   3.573%   $119.9375   $119.94   $119.95   $119.90  
  Purchase #4 $89.26   6.710%   $95.2493   $95.25   $95.25   $95.20  
  Purchase #5 $245.53   4.498%   $256.5739   $256.57   $256.55   $256.60  
  Purchase #6 $200.33   9.246%   $218.8525   $218.85   $218.85   $218.90  
  Purchase #7 $127.30   6.277%   $135.2906   $135.29   $135.30   $135.30  
  7 purchase totals = $967.67       $1,035.5026   $1,035.50   $1,035.50   $1,035.50