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	$96.44	13.371%	$109.335	$109.34	$109.35	$109.30
Purchase #2	$51.46	6.183%	$54.6418	$54.64	$54.65	$54.60
Purchase #3	$141.52	11.381%	$157.6264	$157.63	$157.65	$157.60
Purchase #4	$106.76	4.294%	$111.3443	$111.34	$111.35	$111.30
Purchase #5	$91.57	6.735%	$97.7372	$97.74	$97.75	$97.70
Purchase #6	$69.89	11.632%	$78.0196	$78.02	$78.00	$78.00
Purchase #7	$25.86	9.387%	$28.2875	$28.29	$28.30	$28.30
7 purchase totals =	$583.50		$636.9918	$637.00	$637.05	$636.80