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	$104.40	6.801%	$111.5002	$111.50	$111.50	$111.50
Purchase #2	$243.83	4.325%	$254.3756	$254.38	$254.40	$254.40
Purchase #3	$206.26	13.288%	$233.6678	$233.67	$233.65	$233.70
Purchase #4	$80.33	4.429%	$83.8878	$83.89	$83.90	$83.90
Purchase #5	$239.53	3.264%	$247.3483	$247.35	$247.35	$247.30
Purchase #6	$57.91	7.402%	$62.1965	$62.20	$62.20	$62.20
Purchase #7	$51.58	6.153%	$54.7537	$54.75	$54.75	$54.80
7 purchase totals =	$983.84		$1,047.7299	$1,047.74	$1,047.75	$1,047.80