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	$14.60	3.493%	$15.11	$15.11	$15.10	$15.10
Purchase #2	$84.31	7.287%	$90.4537	$90.45	$90.45	$90.50
Purchase #3	$236.72	12.152%	$265.4862	$265.49	$265.50	$265.50
Purchase #4	$174.41	9.525%	$191.0226	$191.02	$191.00	$191.00
Purchase #5	$202.72	9.350%	$221.6743	$221.67	$221.65	$221.70
Purchase #6	$98.83	3.695%	$102.4818	$102.48	$102.50	$102.50
Purchase #7	$11.87	13.404%	$13.4611	$13.46	$13.45	$13.50
7 purchase totals =	$823.46		$899.6897	$899.68	$899.65	$899.80