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	$149.87	13.107%	$169.5135	$169.51	$169.50	$169.50
Purchase #2	$62.34	3.104%	$64.275	$64.28	$64.30	$64.30
Purchase #3	$188.78	6.106%	$200.3069	$200.31	$200.30	$200.30
Purchase #4	$161.53	6.580%	$172.1587	$172.16	$172.15	$172.20
Purchase #5	$39.60	3.306%	$40.9092	$40.91	$40.90	$40.90
Purchase #6	$156.71	9.489%	$171.5802	$171.58	$171.60	$171.60
Purchase #7	$207.39	6.358%	$220.5759	$220.58	$220.60	$220.60
7 purchase totals =	$966.22		$1,039.3194	$1,039.33	$1,039.35	$1,039.40