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	$231.46	4.688%	$242.3108	$242.31	$242.30	$242.30
Purchase #2	$35.50	11.315%	$39.5168	$39.52	$39.50	$39.50
Purchase #3	$108.30	9.556%	$118.6491	$118.65	$118.65	$118.60
Purchase #4	$100.48	12.809%	$113.3505	$113.35	$113.35	$113.40
Purchase #5	$128.56	4.171%	$133.9222	$133.92	$133.90	$133.90
Purchase #6	$146.29	4.688%	$153.1481	$153.15	$153.15	$153.10
Purchase #7	$6.57	4.766%	$6.8831	$6.88	$6.90	$6.90
7 purchase totals =	$757.16		$807.7806	$807.78	$807.75	$807.70