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	$80.64	11.779%	$90.1386	$90.14	$90.15	$90.10
Purchase #2	$108.46	9.183%	$118.4199	$118.42	$118.40	$118.40
Purchase #3	$174.59	11.430%	$194.5456	$194.55	$194.55	$194.50
Purchase #4	$74.54	12.503%	$83.8597	$83.86	$83.85	$83.90
Purchase #5	$81.34	13.827%	$92.5869	$92.59	$92.60	$92.60
Purchase #6	$198.88	6.242%	$211.2941	$211.29	$211.30	$211.30
Purchase #7	$100.47	13.237%	$113.7692	$113.77	$113.75	$113.80
7 purchase totals =	$818.92		$904.6140	$904.62	$904.60	$904.60