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	$35.48	6.494%	$37.7841	$37.78	$37.80	$37.80
Purchase #2	$245.86	3.726%	$255.0207	$255.02	$255.00	$255.00
Purchase #3	$24.89	3.790%	$25.8333	$25.83	$25.85	$25.80
Purchase #4	$158.91	13.166%	$179.8321	$179.83	$179.85	$179.80
Purchase #5	$16.27	5.287%	$17.1302	$17.13	$17.15	$17.10
Purchase #6	$158.82	6.174%	$168.6255	$168.63	$168.65	$168.60
Purchase #7	$69.90	10.255%	$77.0682	$77.07	$77.05	$77.10
7 purchase totals =	$710.13		$761.2941	$761.29	$761.35	$761.20