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	$242.61	3.271%	$250.5458	$250.55	$250.55	$250.50
Purchase #2	$200.84	6.653%	$214.2019	$214.20	$214.20	$214.20
Purchase #3	$171.77	7.380%	$184.4466	$184.45	$184.45	$184.40
Purchase #4	$48.26	13.742%	$54.8919	$54.89	$54.90	$54.90
Purchase #5	$232.42	9.502%	$254.5045	$254.50	$254.50	$254.50
Purchase #6	$82.33	12.356%	$92.5027	$92.50	$92.50	$92.50
Purchase #7	$227.59	5.402%	$239.8844	$239.88	$239.90	$239.90
7 purchase totals =	$1,205.82		$1,290.9778	$1,290.97	$1,291.00	$1,290.90