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	$72.38	6.350%	$76.9761	$76.98	$77.00	$77.00
Purchase #2	$28.70	7.663%	$30.8993	$30.90	$30.90	$30.90
Purchase #3	$103.58	9.321%	$113.2347	$113.23	$113.25	$113.20
Purchase #4	$232.83	13.463%	$264.1759	$264.18	$264.20	$264.20
Purchase #5	$82.61	8.260%	$89.4336	$89.43	$89.45	$89.40
Purchase #6	$33.72	10.159%	$37.1456	$37.15	$37.15	$37.10
Purchase #7	$238.50	6.413%	$253.795	$253.80	$253.80	$253.80
7 purchase totals =	$792.32		$865.6602	$865.67	$865.75	$865.60