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	$76.33	6.195%	$81.0586	$81.06	$81.05	$81.10
Purchase #2	$109.57	12.550%	$123.321	$123.32	$123.30	$123.30
Purchase #3	$151.43	6.546%	$161.3426	$161.34	$161.35	$161.30
Purchase #4	$242.61	10.625%	$268.3873	$268.39	$268.40	$268.40
Purchase #5	$100.84	10.841%	$111.7721	$111.77	$111.75	$111.80
Purchase #6	$214.36	6.441%	$228.1669	$228.17	$228.15	$228.20
Purchase #7	$45.31	4.290%	$47.2538	$47.25	$47.25	$47.30
7 purchase totals =	$940.45		$1,021.3023	$1,021.30	$1,021.25	$1,021.40