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	$94.35	6.511%	$100.4931	$100.49	$100.50	$100.50
Purchase #2	$171.60	11.441%	$191.2328	$191.23	$191.25	$191.20
Purchase #3	$222.47	3.742%	$230.7948	$230.79	$230.80	$230.80
Purchase #4	$88.42	6.183%	$93.887	$93.89	$93.90	$93.90
Purchase #5	$176.71	8.448%	$191.6385	$191.64	$191.65	$191.60
Purchase #6	$165.79	9.738%	$181.9346	$181.93	$181.95	$181.90
Purchase #7	$57.42	4.341%	$59.9126	$59.91	$59.90	$59.90
7 purchase totals =	$976.76		$1,049.8934	$1,049.88	$1,049.95	$1,049.80