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	$222.68	5.642%	$235.2436	$235.24	$235.25	$235.20
Purchase #2	$37.67	12.826%	$42.5016	$42.50	$42.50	$42.50
Purchase #3	$160.42	7.230%	$172.0184	$172.02	$172.00	$172.00
Purchase #4	$78.69	7.675%	$84.7295	$84.73	$84.75	$84.70
Purchase #5	$78.89	5.243%	$83.0262	$83.03	$83.05	$83.00
Purchase #6	$81.64	9.753%	$89.6023	$89.60	$89.60	$89.60
Purchase #7	$168.71	7.137%	$180.7508	$180.75	$180.75	$180.80
7 purchase totals =	$828.70		$887.8724	$887.87	$887.90	$887.80