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	$115.92	4.180%	$120.7655	$120.77	$120.75	$120.80
Purchase #2	$107.82	3.579%	$111.6789	$111.68	$111.70	$111.70
Purchase #3	$70.73	7.317%	$75.9053	$75.91	$75.90	$75.90
Purchase #4	$40.53	6.587%	$43.1997	$43.20	$43.20	$43.20
Purchase #5	$73.91	12.184%	$82.9152	$82.92	$82.90	$82.90
Purchase #6	$201.30	8.471%	$218.3521	$218.35	$218.35	$218.40
Purchase #7	$164.68	12.574%	$185.3869	$185.39	$185.40	$185.40
7 purchase totals =	$774.89		$838.2036	$838.22	$838.20	$838.30