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	$236.92	11.666%	$264.5591	$264.56	$264.55	$264.60
Purchase #2	$100.84	3.654%	$104.5247	$104.52	$104.50	$104.50
Purchase #3	$78.33	3.548%	$81.1091	$81.11	$81.10	$81.10
Purchase #4	$78.46	13.271%	$88.8724	$88.87	$88.85	$88.90
Purchase #5	$95.92	12.512%	$107.9215	$107.92	$107.90	$107.90
Purchase #6	$246.51	6.339%	$262.1363	$262.14	$262.15	$262.10
Purchase #7	$86.59	13.848%	$98.581	$98.58	$98.60	$98.60
7 purchase totals =	$923.57		$1,007.7041	$1,007.70	$1,007.65	$1,007.70