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	$136.43	7.291%	$146.3771	$146.38	$146.40	$146.40
Purchase #2	$188.40	9.667%	$206.6126	$206.61	$206.60	$206.60
Purchase #3	$250.25	12.641%	$281.8841	$281.88	$281.90	$281.90
Purchase #4	$92.69	8.537%	$100.6029	$100.60	$100.60	$100.60
Purchase #5	$238.93	4.194%	$248.9507	$248.95	$248.95	$249.00
Purchase #6	$9.41	11.296%	$10.473	$10.47	$10.45	$10.50
Purchase #7	$165.88	8.263%	$179.5867	$179.59	$179.60	$179.60
7 purchase totals =	$1,081.99		$1,174.4871	$1,174.48	$1,174.50	$1,174.60