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	$39.40	8.567%	$42.7754	$42.78	$42.80	$42.80
Purchase #2	$11.39	10.137%	$12.5446	$12.54	$12.55	$12.50
Purchase #3	$37.63	11.612%	$41.9996	$42.00	$42.00	$42.00
Purchase #4	$78.94	13.614%	$89.6869	$89.69	$89.70	$89.70
Purchase #5	$90.77	12.306%	$101.9402	$101.94	$101.95	$101.90
Purchase #6	$47.86	6.580%	$51.0092	$51.01	$51.00	$51.00
Purchase #7	$204.66	4.808%	$214.5001	$214.50	$214.50	$214.50
7 purchase totals =	$510.65		$554.4560	$554.46	$554.50	$554.40