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	$50.28	13.669%	$57.1528	$57.15	$57.15	$57.20
Purchase #2	$178.85	3.615%	$185.3154	$185.32	$185.30	$185.30
Purchase #3	$219.77	9.508%	$240.6657	$240.67	$240.65	$240.70
Purchase #4	$19.62	5.660%	$20.7305	$20.73	$20.75	$20.70
Purchase #5	$47.59	10.268%	$52.4765	$52.48	$52.50	$52.50
Purchase #6	$50.72	4.331%	$52.9167	$52.92	$52.90	$52.90
Purchase #7	$229.84	6.688%	$245.2117	$245.21	$245.20	$245.20
7 purchase totals =	$796.67		$854.4693	$854.48	$854.45	$854.50