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	$82.57	8.787%	$89.8254	$89.83	$89.85	$89.80
Purchase #2	$247.25	4.401%	$258.1315	$258.13	$258.15	$258.10
Purchase #3	$124.49	10.365%	$137.3934	$137.39	$137.40	$137.40
Purchase #4	$59.58	4.199%	$62.0818	$62.08	$62.10	$62.10
Purchase #5	$98.52	5.592%	$104.0292	$104.03	$104.05	$104.00
Purchase #6	$60.51	10.414%	$66.8115	$66.81	$66.80	$66.80
Purchase #7	$245.71	9.388%	$268.7773	$268.78	$268.80	$268.80
7 purchase totals =	$918.63		$987.0501	$987.05	$987.15	$987.00