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	$33.45	7.219%	$35.8648	$35.86	$35.85	$35.90
Purchase #2	$186.95	6.734%	$199.5392	$199.54	$199.55	$199.50
Purchase #3	$42.69	6.311%	$45.3842	$45.38	$45.40	$45.40
Purchase #4	$114.62	4.543%	$119.8272	$119.83	$119.85	$119.80
Purchase #5	$88.61	5.577%	$93.5518	$93.55	$93.55	$93.60
Purchase #6	$203.97	9.762%	$223.8816	$223.88	$223.90	$223.90
Purchase #7	$125.89	12.791%	$141.9926	$141.99	$142.00	$142.00
7 purchase totals =	$796.18		$860.0414	$860.03	$860.10	$860.10