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	$190.31	9.397%	$208.1934	$208.19	$208.20	$208.20
Purchase #2	$103.89	5.662%	$109.7723	$109.77	$109.75	$109.80
Purchase #3	$226.38	12.313%	$254.2542	$254.25	$254.25	$254.30
Purchase #4	$39.51	4.769%	$41.3942	$41.39	$41.40	$41.40
Purchase #5	$19.75	7.420%	$21.2155	$21.22	$21.20	$21.20
Purchase #6	$223.28	13.780%	$254.048	$254.05	$254.05	$254.00
Purchase #7	$97.49	8.157%	$105.4423	$105.44	$105.45	$105.40
7 purchase totals =	$900.61		$994.3199	$994.31	$994.30	$994.30