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	$72.84	9.134%	$79.4932	$79.49	$79.50	$79.50
Purchase #2	$52.37	9.825%	$57.5154	$57.52	$57.50	$57.50
Purchase #3	$210.54	5.505%	$222.1302	$222.13	$222.15	$222.10
Purchase #4	$176.63	13.231%	$199.9999	$200.00	$200.00	$200.00
Purchase #5	$125.86	6.561%	$134.1177	$134.12	$134.10	$134.10
Purchase #6	$112.70	9.339%	$123.2251	$123.23	$123.25	$123.20
Purchase #7	$34.91	7.602%	$37.5639	$37.56	$37.55	$37.60
7 purchase totals =	$785.85		$854.0454	$854.05	$854.05	$854.00