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	$19.83	4.741%	$20.7701	$20.77	$20.75	$20.80
Purchase #2	$148.40	13.829%	$168.9222	$168.92	$168.90	$168.90
Purchase #3	$174.88	7.442%	$187.8946	$187.89	$187.90	$187.90
Purchase #4	$250.74	5.383%	$264.2373	$264.24	$264.25	$264.20
Purchase #5	$158.50	4.482%	$165.604	$165.60	$165.60	$165.60
Purchase #6	$160.82	8.103%	$173.8512	$173.85	$173.85	$173.90
Purchase #7	$98.59	13.757%	$112.153	$112.15	$112.15	$112.20
7 purchase totals =	$1,011.76		$1,093.4324	$1,093.42	$1,093.40	$1,093.50