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	$41.87	6.701%	$44.6757	$44.68	$44.70	$44.70
Purchase #2	$211.89	5.180%	$222.8659	$222.87	$222.85	$222.90
Purchase #3	$120.35	6.364%	$128.0091	$128.01	$128.00	$128.00
Purchase #4	$122.79	7.265%	$131.7107	$131.71	$131.70	$131.70
Purchase #5	$32.97	13.475%	$37.4127	$37.41	$37.40	$37.40
Purchase #6	$238.69	11.410%	$265.9245	$265.92	$265.90	$265.90
Purchase #7	$143.51	5.393%	$151.2495	$151.25	$151.25	$151.20
7 purchase totals =	$912.07		$981.8481	$981.85	$981.80	$981.80