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	$140.96	10.394%	$155.6114	$155.61	$155.60	$155.60
Purchase #2	$97.63	10.327%	$107.7123	$107.71	$107.70	$107.70
Purchase #3	$228.28	9.613%	$250.2246	$250.22	$250.20	$250.20
Purchase #4	$103.29	8.673%	$112.2483	$112.25	$112.25	$112.20
Purchase #5	$188.56	3.437%	$195.0408	$195.04	$195.05	$195.00
Purchase #6	$55.41	6.792%	$59.1734	$59.17	$59.15	$59.20
Purchase #7	$10.73	6.801%	$11.4597	$11.46	$11.45	$11.50
7 purchase totals =	$824.86		$891.4705	$891.46	$891.40	$891.40