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	$79.58	13.674%	$90.4618	$90.46	$90.45	$90.50
Purchase #2	$79.67	3.303%	$82.3015	$82.30	$82.30	$82.30
Purchase #3	$12.74	8.764%	$13.8565	$13.86	$13.85	$13.90
Purchase #4	$228.32	11.685%	$254.9992	$255.00	$255.00	$255.00
Purchase #5	$249.50	9.682%	$273.6566	$273.66	$273.65	$273.70
Purchase #6	$39.29	9.361%	$42.9679	$42.97	$42.95	$43.00
Purchase #7	$93.33	9.573%	$102.2645	$102.26	$102.25	$102.30
7 purchase totals =	$782.43		$860.5080	$860.51	$860.45	$860.70