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	$50.82	6.481%	$54.1136	$54.11	$54.10	$54.10
Purchase #2	$170.59	8.592%	$185.2471	$185.25	$185.25	$185.20
Purchase #3	$131.38	6.594%	$140.0432	$140.04	$140.05	$140.00
Purchase #4	$74.45	4.493%	$77.795	$77.80	$77.80	$77.80
Purchase #5	$154.25	9.417%	$168.7757	$168.78	$168.80	$168.80
Purchase #6	$57.74	12.812%	$65.1376	$65.14	$65.15	$65.10
Purchase #7	$91.71	7.147%	$98.2645	$98.26	$98.25	$98.30
7 purchase totals =	$730.94		$789.3767	$789.38	$789.40	$789.30