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	$18.73	5.253%	$19.7139	$19.71	$19.70	$19.70
Purchase #2	$78.26	5.841%	$82.8312	$82.83	$82.85	$82.80
Purchase #3	$162.36	11.582%	$181.1645	$181.16	$181.15	$181.20
Purchase #4	$38.68	10.638%	$42.7948	$42.79	$42.80	$42.80
Purchase #5	$66.64	10.331%	$73.5246	$73.52	$73.50	$73.50
Purchase #6	$48.45	6.828%	$51.7582	$51.76	$51.75	$51.80
Purchase #7	$58.30	3.745%	$60.4833	$60.48	$60.50	$60.50
7 purchase totals =	$471.42		$512.2705	$512.25	$512.25	$512.30