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	$89.54	10.565%	$98.9999	$99.00	$99.00	$99.00
Purchase #2	$247.72	4.451%	$258.746	$258.75	$258.75	$258.70
Purchase #3	$82.37	8.375%	$89.2685	$89.27	$89.25	$89.30
Purchase #4	$157.44	4.523%	$164.561	$164.56	$164.55	$164.60
Purchase #5	$245.86	12.245%	$275.9656	$275.97	$275.95	$276.00
Purchase #6	$104.32	9.331%	$114.0541	$114.05	$114.05	$114.10
Purchase #7	$55.66	3.375%	$57.5385	$57.54	$57.55	$57.50
7 purchase totals =	$982.91		$1,059.1336	$1,059.14	$1,059.10	$1,059.20