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	$140.67	13.329%	$159.4199	$159.42	$159.40	$159.40
Purchase #2	$129.52	11.839%	$144.8539	$144.85	$144.85	$144.90
Purchase #3	$125.93	3.469%	$130.2985	$130.30	$130.30	$130.30
Purchase #4	$36.57	4.271%	$38.1319	$38.13	$38.15	$38.10
Purchase #5	$213.86	12.575%	$240.7529	$240.75	$240.75	$240.80
Purchase #6	$212.39	5.184%	$223.4003	$223.40	$223.40	$223.40
Purchase #7	$189.31	12.701%	$213.3543	$213.35	$213.35	$213.40
7 purchase totals =	$1,048.25		$1,150.2117	$1,150.20	$1,150.20	$1,150.30