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	$26.75	6.467%	$28.4799	$28.48	$28.50	$28.50
Purchase #2	$18.82	7.784%	$20.2849	$20.28	$20.30	$20.30
Purchase #3	$216.80	11.226%	$241.138	$241.14	$241.15	$241.10
Purchase #4	$80.95	10.190%	$89.1988	$89.20	$89.20	$89.20
Purchase #5	$24.44	12.765%	$27.5598	$27.56	$27.55	$27.60
Purchase #6	$162.37	7.553%	$174.6338	$174.63	$174.65	$174.60
Purchase #7	$49.69	9.543%	$54.4319	$54.43	$54.45	$54.40
7 purchase totals =	$579.82		$635.7271	$635.72	$635.80	$635.70