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 $177.35   13.867%   $201.9431   $201.94   $201.95   $201.90  
  Purchase #2 $60.27   6.120%   $63.9585   $63.96   $63.95   $64.00  
  Purchase #3 $63.25   9.549%   $69.2897   $69.29   $69.30   $69.30  
  Purchase #4 $195.31   10.538%   $215.8918   $215.89   $215.90   $215.90  
  Purchase #5 $22.46   10.864%   $24.9001   $24.90   $24.90   $24.90  
  Purchase #6 $249.94   6.863%   $267.0934   $267.09   $267.10   $267.10  
  Purchase #7 $176.54   3.782%   $183.2167   $183.22   $183.20   $183.20  
  7 purchase totals = $945.12       $1,026.2933   $1,026.29   $1,026.30   $1,026.30