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	$123.27	4.320%	$128.5953	$128.60	$128.60	$128.60
Purchase #2	$83.49	9.272%	$91.2312	$91.23	$91.25	$91.20
Purchase #3	$77.91	3.336%	$80.5091	$80.51	$80.50	$80.50
Purchase #4	$161.59	6.748%	$172.4941	$172.49	$172.50	$172.50
Purchase #5	$241.84	9.387%	$264.5415	$264.54	$264.55	$264.50
Purchase #6	$68.77	3.852%	$71.419	$71.42	$71.40	$71.40
Purchase #7	$85.67	7.489%	$92.0858	$92.09	$92.10	$92.10
7 purchase totals =	$842.54		$900.8760	$900.88	$900.90	$900.80