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	$123.72	10.846%	$137.1387	$137.14	$137.15	$137.10
Purchase #2	$74.60	10.255%	$82.2502	$82.25	$82.25	$82.30
Purchase #3	$63.92	5.131%	$67.1997	$67.20	$67.20	$67.20
Purchase #4	$139.91	12.116%	$156.8615	$156.86	$156.85	$156.90
Purchase #5	$31.37	7.824%	$33.8244	$33.82	$33.80	$33.80
Purchase #6	$45.36	10.713%	$50.2194	$50.22	$50.20	$50.20
Purchase #7	$143.92	8.224%	$155.756	$155.76	$155.75	$155.80
7 purchase totals =	$622.80		$683.2499	$683.25	$683.20	$683.30