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	$11.71	6.591%	$12.4818	$12.48	$12.50	$12.50
Purchase #2	$146.76	6.428%	$156.1937	$156.19	$156.20	$156.20
Purchase #3	$173.61	13.297%	$196.6949	$196.69	$196.70	$196.70
Purchase #4	$244.65	11.841%	$273.619	$273.62	$273.60	$273.60
Purchase #5	$136.58	7.234%	$146.4602	$146.46	$146.45	$146.50
Purchase #6	$165.58	11.247%	$184.2028	$184.20	$184.20	$184.20
Purchase #7	$87.88	5.230%	$92.4761	$92.48	$92.50	$92.50
7 purchase totals =	$966.77		$1,062.1285	$1,062.12	$1,062.15	$1,062.20