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	$39.84	7.228%	$42.7196	$42.72	$42.70	$42.70
Purchase #2	$55.29	3.707%	$57.3396	$57.34	$57.35	$57.30
Purchase #3	$126.95	13.721%	$144.3688	$144.37	$144.35	$144.40
Purchase #4	$173.33	3.193%	$178.8644	$178.86	$178.85	$178.90
Purchase #5	$168.52	6.270%	$179.0862	$179.09	$179.10	$179.10
Purchase #6	$198.26	10.727%	$219.5274	$219.53	$219.55	$219.50
Purchase #7	$231.73	4.358%	$241.8288	$241.83	$241.85	$241.80
7 purchase totals =	$993.92		$1,063.7348	$1,063.74	$1,063.75	$1,063.70