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	$120.69	5.550%	$127.3883	$127.39	$127.40	$127.40
Purchase #2	$214.45	13.869%	$244.1921	$244.19	$244.20	$244.20
Purchase #3	$130.58	10.575%	$144.3888	$144.39	$144.40	$144.40
Purchase #4	$200.66	4.642%	$209.9746	$209.97	$209.95	$210.00
Purchase #5	$213.33	12.317%	$239.6059	$239.61	$239.60	$239.60
Purchase #6	$209.58	11.389%	$233.4491	$233.45	$233.45	$233.40
Purchase #7	$129.29	9.417%	$141.4652	$141.47	$141.45	$141.50
7 purchase totals =	$1,218.58		$1,340.4640	$1,340.47	$1,340.45	$1,340.50