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	$51.33	6.136%	$54.4796	$54.48	$54.50	$54.50
Purchase #2	$183.26	9.461%	$200.5982	$200.60	$200.60	$200.60
Purchase #3	$186.52	13.771%	$212.2057	$212.21	$212.20	$212.20
Purchase #4	$248.37	10.164%	$273.6143	$273.61	$273.60	$273.60
Purchase #5	$127.57	13.448%	$144.7256	$144.73	$144.75	$144.70
Purchase #6	$211.62	8.604%	$229.8278	$229.83	$229.85	$229.80
Purchase #7	$165.33	11.581%	$184.4769	$184.48	$184.50	$184.50
7 purchase totals =	$1,174.00		$1,299.9281	$1,299.94	$1,300.00	$1,299.90