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	$20.44	9.137%	$22.3076	$22.31	$22.30	$22.30
Purchase #2	$61.61	7.714%	$66.3626	$66.36	$66.35	$66.40
Purchase #3	$40.35	7.866%	$43.5239	$43.52	$43.50	$43.50
Purchase #4	$239.56	4.489%	$250.3138	$250.31	$250.30	$250.30
Purchase #5	$107.50	4.724%	$112.5783	$112.58	$112.60	$112.60
Purchase #6	$54.54	12.398%	$61.3019	$61.30	$61.30	$61.30
Purchase #7	$169.25	7.738%	$182.3466	$182.35	$182.35	$182.30
7 purchase totals =	$693.25		$738.7347	$738.73	$738.70	$738.70