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	$74.46	4.501%	$77.8114	$77.81	$77.80	$77.80
Purchase #2	$152.88	8.675%	$166.1423	$166.14	$166.15	$166.10
Purchase #3	$64.95	3.766%	$67.396	$67.40	$67.40	$67.40
Purchase #4	$104.33	9.685%	$114.4344	$114.43	$114.45	$114.40
Purchase #5	$153.55	9.438%	$168.042	$168.04	$168.05	$168.00
Purchase #6	$37.25	12.160%	$41.7796	$41.78	$41.80	$41.80
Purchase #7	$33.74	6.205%	$35.8336	$35.83	$35.85	$35.80
7 purchase totals =	$621.16		$671.4393	$671.43	$671.50	$671.30