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 $182.32   11.856%   $203.9359   $203.94   $203.95   $203.90  
  Purchase #2 $7.77   6.240%   $8.2548   $8.25   $8.25   $8.30  
  Purchase #3 $75.66   5.194%   $79.5898   $79.59   $79.60   $79.60  
  Purchase #4 $94.90   3.782%   $98.4891   $98.49   $98.50   $98.50  
  Purchase #5 $226.61   6.544%   $241.4394   $241.44   $241.45   $241.40  
  Purchase #6 $133.50   9.739%   $146.5016   $146.50   $146.50   $146.50  
  Purchase #7 $131.32   12.351%   $147.5393   $147.54   $147.55   $147.50  
  7 purchase totals = $852.08       $925.7499   $925.75   $925.80   $925.70