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	$84.89	4.513%	$88.7211	$88.72	$88.70	$88.70
Purchase #2	$35.77	12.108%	$40.101	$40.10	$40.10	$40.10
Purchase #3	$159.86	9.506%	$175.0563	$175.06	$175.05	$175.10
Purchase #4	$66.91	8.137%	$72.3545	$72.35	$72.35	$72.40
Purchase #5	$110.71	7.322%	$118.8162	$118.82	$118.80	$118.80
Purchase #6	$47.98	6.593%	$51.1433	$51.14	$51.15	$51.10
Purchase #7	$165.86	9.249%	$181.2004	$181.20	$181.20	$181.20
7 purchase totals =	$671.98		$727.3928	$727.39	$727.35	$727.40