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	$233.91	13.552%	$265.6095	$265.61	$265.60	$265.60
Purchase #2	$123.62	5.524%	$130.4488	$130.45	$130.45	$130.40
Purchase #3	$35.67	4.451%	$37.2577	$37.26	$37.25	$37.30
Purchase #4	$123.94	10.523%	$136.9822	$136.98	$137.00	$137.00
Purchase #5	$34.69	3.224%	$35.8084	$35.81	$35.80	$35.80
Purchase #6	$48.67	12.728%	$54.8647	$54.86	$54.85	$54.90
Purchase #7	$179.26	9.658%	$196.5729	$196.57	$196.55	$196.60
7 purchase totals =	$779.76		$857.5442	$857.54	$857.50	$857.60