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	$201.39	13.658%	$228.8958	$228.90	$228.90	$228.90
Purchase #2	$234.72	4.411%	$245.0735	$245.07	$245.05	$245.10
Purchase #3	$149.58	10.644%	$165.5013	$165.50	$165.50	$165.50
Purchase #4	$210.47	3.399%	$217.6239	$217.62	$217.60	$217.60
Purchase #5	$69.86	12.212%	$78.3913	$78.39	$78.40	$78.40
Purchase #6	$165.93	10.502%	$183.356	$183.36	$183.35	$183.40
Purchase #7	$238.46	13.665%	$271.0456	$271.05	$271.05	$271.00
7 purchase totals =	$1,270.41		$1,389.8874	$1,389.89	$1,389.85	$1,389.90