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	$71.52	12.450%	$80.4242	$80.42	$80.40	$80.40
Purchase #2	$134.40	4.719%	$140.7423	$140.74	$140.75	$140.70
Purchase #3	$209.65	9.687%	$229.9588	$229.96	$229.95	$230.00
Purchase #4	$78.86	6.172%	$83.7272	$83.73	$83.75	$83.70
Purchase #5	$206.55	6.543%	$220.0646	$220.06	$220.05	$220.10
Purchase #6	$145.71	7.377%	$156.459	$156.46	$156.45	$156.50
Purchase #7	$128.90	13.585%	$146.4111	$146.41	$146.40	$146.40
7 purchase totals =	$975.59		$1,057.7872	$1,057.78	$1,057.75	$1,057.80