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	$64.35	13.155%	$72.8152	$72.82	$72.80	$72.80
Purchase #2	$98.71	4.103%	$102.7601	$102.76	$102.75	$102.80
Purchase #3	$159.50	13.658%	$181.2845	$181.28	$181.30	$181.30
Purchase #4	$250.33	7.294%	$268.5891	$268.59	$268.60	$268.60
Purchase #5	$196.28	9.187%	$214.3122	$214.31	$214.30	$214.30
Purchase #6	$206.94	10.683%	$229.0474	$229.05	$229.05	$229.00
Purchase #7	$79.97	6.477%	$85.1497	$85.15	$85.15	$85.10
7 purchase totals =	$1,056.08		$1,153.9582	$1,153.96	$1,153.95	$1,153.90