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	$116.52	9.584%	$127.6873	$127.69	$127.70	$127.70
Purchase #2	$107.79	3.409%	$111.4646	$111.46	$111.45	$111.50
Purchase #3	$20.26	6.298%	$21.536	$21.54	$21.55	$21.50
Purchase #4	$38.50	11.400%	$42.889	$42.89	$42.90	$42.90
Purchase #5	$40.42	12.150%	$45.331	$45.33	$45.35	$45.30
Purchase #6	$55.39	7.426%	$59.5033	$59.50	$59.50	$59.50
Purchase #7	$225.41	3.762%	$233.8899	$233.89	$233.90	$233.90
7 purchase totals =	$604.29		$642.3011	$642.30	$642.35	$642.30