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	$20.58	4.139%	$21.4318	$21.43	$21.45	$21.40
Purchase #2	$60.79	11.601%	$67.8422	$67.84	$67.85	$67.80
Purchase #3	$136.64	6.290%	$145.2347	$145.23	$145.25	$145.20
Purchase #4	$108.39	3.219%	$111.8791	$111.88	$111.90	$111.90
Purchase #5	$92.60	3.494%	$95.8354	$95.84	$95.85	$95.80
Purchase #6	$88.90	13.766%	$101.138	$101.14	$101.15	$101.10
Purchase #7	$224.96	5.165%	$236.5792	$236.58	$236.60	$236.60
7 purchase totals =	$732.86		$779.9404	$779.94	$780.05	$779.80