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	$242.35	12.438%	$272.4935	$272.49	$272.50	$272.50
Purchase #2	$71.41	6.633%	$76.1466	$76.15	$76.15	$76.10
Purchase #3	$228.97	6.149%	$243.0494	$243.05	$243.05	$243.00
Purchase #4	$92.82	4.672%	$97.1566	$97.16	$97.15	$97.20
Purchase #5	$35.34	6.222%	$37.5389	$37.54	$37.55	$37.50
Purchase #6	$50.56	9.417%	$55.3212	$55.32	$55.30	$55.30
Purchase #7	$96.83	4.242%	$100.9375	$100.94	$100.95	$100.90
7 purchase totals =	$818.28		$882.6437	$882.65	$882.65	$882.50