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	$247.82	10.355%	$273.4818	$273.48	$273.50	$273.50
Purchase #2	$151.34	13.406%	$171.6286	$171.63	$171.65	$171.60
Purchase #3	$19.78	12.156%	$22.1845	$22.18	$22.20	$22.20
Purchase #4	$153.27	10.715%	$169.6929	$169.69	$169.70	$169.70
Purchase #5	$59.26	4.508%	$61.9314	$61.93	$61.95	$61.90
Purchase #6	$19.91	7.627%	$21.4285	$21.43	$21.45	$21.40
Purchase #7	$99.30	6.529%	$105.7833	$105.78	$105.80	$105.80
7 purchase totals =	$750.68		$826.1310	$826.12	$826.25	$826.10