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	$204.85	6.498%	$218.1612	$218.16	$218.15	$218.20
Purchase #2	$69.59	3.618%	$72.1078	$72.11	$72.10	$72.10
Purchase #3	$75.29	13.472%	$85.4331	$85.43	$85.45	$85.40
Purchase #4	$78.33	11.845%	$87.6082	$87.61	$87.60	$87.60
Purchase #5	$246.54	13.496%	$279.813	$279.81	$279.80	$279.80
Purchase #6	$81.50	5.815%	$86.2392	$86.24	$86.25	$86.20
Purchase #7	$64.75	7.252%	$69.4457	$69.45	$69.45	$69.40
7 purchase totals =	$820.85		$898.8082	$898.81	$898.80	$898.70