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	$138.97	6.571%	$148.1017	$148.10	$148.10	$148.10
Purchase #2	$89.66	10.540%	$99.1102	$99.11	$99.10	$99.10
Purchase #3	$139.30	8.159%	$150.6655	$150.67	$150.65	$150.70
Purchase #4	$73.56	5.724%	$77.7706	$77.77	$77.75	$77.80
Purchase #5	$143.41	3.650%	$148.6445	$148.64	$148.65	$148.60
Purchase #6	$173.84	5.209%	$182.8953	$182.90	$182.90	$182.90
Purchase #7	$150.44	12.149%	$168.717	$168.72	$168.70	$168.70
7 purchase totals =	$909.18		$975.9048	$975.91	$975.85	$975.90