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	$12.25	4.247%	$12.7703	$12.77	$12.75	$12.80
Purchase #2	$135.77	7.844%	$146.4198	$146.42	$146.40	$146.40
Purchase #3	$46.96	5.453%	$49.5207	$49.52	$49.50	$49.50
Purchase #4	$32.25	9.731%	$35.3882	$35.39	$35.40	$35.40
Purchase #5	$239.59	10.330%	$264.3396	$264.34	$264.35	$264.30
Purchase #6	$160.97	10.764%	$178.2968	$178.30	$178.30	$178.30
Purchase #7	$247.42	3.362%	$255.7383	$255.74	$255.75	$255.70
7 purchase totals =	$875.21		$942.4737	$942.48	$942.45	$942.40