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	$111.66	10.365%	$123.2336	$123.23	$123.25	$123.20
Purchase #2	$215.70	3.394%	$223.0209	$223.02	$223.00	$223.00
Purchase #3	$42.98	13.190%	$48.6491	$48.65	$48.65	$48.60
Purchase #4	$207.53	11.574%	$231.5495	$231.55	$231.55	$231.50
Purchase #5	$147.67	5.301%	$155.498	$155.50	$155.50	$155.50
Purchase #6	$18.91	9.277%	$20.6643	$20.66	$20.65	$20.70
Purchase #7	$80.65	10.869%	$89.4158	$89.42	$89.40	$89.40
7 purchase totals =	$825.10		$892.0312	$892.03	$892.00	$891.90