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	$79.92	12.461%	$89.8788	$89.88	$89.90	$89.90
Purchase #2	$40.34	8.501%	$43.7693	$43.77	$43.75	$43.80
Purchase #3	$248.95	10.322%	$274.6466	$274.65	$274.65	$274.60
Purchase #4	$169.90	10.165%	$187.1703	$187.17	$187.15	$187.20
Purchase #5	$196.78	8.165%	$212.8471	$212.85	$212.85	$212.80
Purchase #6	$220.88	3.502%	$228.6152	$228.62	$228.60	$228.60
Purchase #7	$41.87	7.770%	$45.1233	$45.12	$45.10	$45.10
7 purchase totals =	$998.64		$1,082.0506	$1,082.06	$1,082.00	$1,082.00