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	$75.65	10.425%	$83.5365	$83.54	$83.55	$83.50
Purchase #2	$145.34	13.616%	$165.1295	$165.13	$165.15	$165.10
Purchase #3	$59.79	3.578%	$61.9293	$61.93	$61.95	$61.90
Purchase #4	$133.90	9.324%	$146.3848	$146.38	$146.40	$146.40
Purchase #5	$102.67	10.792%	$113.7501	$113.75	$113.75	$113.80
Purchase #6	$92.99	13.183%	$105.2489	$105.25	$105.25	$105.20
Purchase #7	$159.83	12.761%	$180.2259	$180.23	$180.25	$180.20
7 purchase totals =	$770.17		$856.2050	$856.21	$856.30	$856.10