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	$83.39	9.108%	$90.9852	$90.99	$91.00	$91.00
Purchase #2	$120.54	5.287%	$126.9129	$126.91	$126.90	$126.90
Purchase #3	$95.83	4.230%	$99.8836	$99.88	$99.90	$99.90
Purchase #4	$31.72	3.209%	$32.7379	$32.74	$32.75	$32.70
Purchase #5	$132.40	3.745%	$137.3584	$137.36	$137.35	$137.40
Purchase #6	$131.38	12.416%	$147.6921	$147.69	$147.70	$147.70
Purchase #7	$75.29	9.847%	$82.7038	$82.70	$82.70	$82.70
7 purchase totals =	$670.55		$718.2739	$718.27	$718.30	$718.30