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	$205.52	3.375%	$212.4563	$212.46	$212.45	$212.50
Purchase #2	$90.39	7.410%	$97.0879	$97.09	$97.10	$97.10
Purchase #3	$135.82	7.163%	$145.5488	$145.55	$145.55	$145.50
Purchase #4	$18.54	7.334%	$19.8997	$19.90	$19.90	$19.90
Purchase #5	$220.25	13.739%	$250.5101	$250.51	$250.50	$250.50
Purchase #6	$78.69	8.586%	$85.4463	$85.45	$85.45	$85.40
Purchase #7	$50.83	12.603%	$57.2361	$57.24	$57.25	$57.20
7 purchase totals =	$800.04		$868.1852	$868.20	$868.20	$868.10