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	$80.86	9.294%	$88.3751	$88.38	$88.40	$88.40
Purchase #2	$32.71	13.197%	$37.0267	$37.03	$37.05	$37.00
Purchase #3	$163.37	5.608%	$172.5318	$172.53	$172.55	$172.50
Purchase #4	$193.88	11.229%	$215.6508	$215.65	$215.65	$215.70
Purchase #5	$165.39	7.558%	$177.8902	$177.89	$177.90	$177.90
Purchase #6	$41.89	8.748%	$45.5545	$45.55	$45.55	$45.60
Purchase #7	$175.65	8.863%	$191.2179	$191.22	$191.20	$191.20
7 purchase totals =	$853.75		$928.2470	$928.25	$928.30	$928.30