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	$121.82	5.158%	$128.1035	$128.10	$128.10	$128.10
Purchase #2	$21.75	10.856%	$24.1112	$24.11	$24.10	$24.10
Purchase #3	$38.49	11.766%	$43.0187	$43.02	$43.00	$43.00
Purchase #4	$159.74	5.479%	$168.4922	$168.49	$168.50	$168.50
Purchase #5	$66.92	6.517%	$71.2812	$71.28	$71.30	$71.30
Purchase #6	$76.30	4.700%	$79.8861	$79.89	$79.90	$79.90
Purchase #7	$101.51	7.250%	$108.8695	$108.87	$108.85	$108.90
7 purchase totals =	$586.53		$623.7624	$623.76	$623.75	$623.80