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	$94.83	8.757%	$103.1343	$103.13	$103.15	$103.10
Purchase #2	$22.27	13.334%	$25.2395	$25.24	$25.25	$25.20
Purchase #3	$165.56	13.744%	$188.3146	$188.31	$188.30	$188.30
Purchase #4	$194.61	10.658%	$215.3515	$215.35	$215.35	$215.40
Purchase #5	$51.87	3.433%	$53.6507	$53.65	$53.65	$53.70
Purchase #6	$157.39	9.377%	$172.1485	$172.15	$172.15	$172.10
Purchase #7	$81.95	6.223%	$87.0497	$87.05	$87.05	$87.00
7 purchase totals =	$768.48		$844.8888	$844.88	$844.90	$844.80