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 $204.75   12.695%   $230.743   $230.74   $230.75   $230.70  
  Purchase #2 $55.62   8.152%   $60.1541   $60.15   $60.15   $60.20  
  Purchase #3 $245.54   5.299%   $258.5512   $258.55   $258.55   $258.60  
  Purchase #4 $41.85   13.534%   $47.514   $47.51   $47.50   $47.50  
  Purchase #5 $44.88   10.707%   $49.6853   $49.69   $49.70   $49.70  
  Purchase #6 $185.26   6.665%   $197.6076   $197.61   $197.60   $197.60  
  Purchase #7 $82.81   13.529%   $94.0134   $94.01   $94.00   $94.00  
  7 purchase totals = $860.71       $938.2686   $938.26   $938.25   $938.30