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	$65.86	10.837%	$72.9972	$73.00	$73.00	$73.00
Purchase #2	$214.57	13.742%	$244.0562	$244.06	$244.05	$244.10
Purchase #3	$131.97	5.424%	$139.1281	$139.13	$139.15	$139.10
Purchase #4	$142.85	8.672%	$155.238	$155.24	$155.25	$155.20
Purchase #5	$168.91	9.795%	$185.4547	$185.45	$185.45	$185.50
Purchase #6	$91.68	8.317%	$99.305	$99.31	$99.30	$99.30
Purchase #7	$69.40	11.865%	$77.6343	$77.63	$77.65	$77.60
7 purchase totals =	$885.24		$973.8135	$973.82	$973.85	$973.80