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	$89.72	11.597%	$100.1248	$100.12	$100.10	$100.10
Purchase #2	$234.64	12.219%	$263.3107	$263.31	$263.30	$263.30
Purchase #3	$108.44	8.539%	$117.6997	$117.70	$117.70	$117.70
Purchase #4	$125.61	13.509%	$142.5787	$142.58	$142.60	$142.60
Purchase #5	$69.33	11.470%	$77.2822	$77.28	$77.30	$77.30
Purchase #6	$202.76	6.656%	$216.2557	$216.26	$216.25	$216.30
Purchase #7	$140.81	8.181%	$152.3297	$152.33	$152.35	$152.30
7 purchase totals =	$971.31		$1,069.5815	$1,069.58	$1,069.60	$1,069.60