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	$99.64	12.324%	$111.9196	$111.92	$111.90	$111.90
Purchase #2	$174.75	9.823%	$191.9157	$191.92	$191.90	$191.90
Purchase #3	$64.56	11.161%	$71.7655	$71.77	$71.75	$71.80
Purchase #4	$22.89	7.638%	$24.6383	$24.64	$24.65	$24.60
Purchase #5	$196.70	7.582%	$211.6138	$211.61	$211.60	$211.60
Purchase #6	$37.81	13.686%	$42.9847	$42.98	$43.00	$43.00
Purchase #7	$134.43	13.358%	$152.3872	$152.39	$152.40	$152.40
7 purchase totals =	$730.78		$807.2248	$807.23	$807.20	$807.20