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	$49.56	10.122%	$54.5765	$54.58	$54.60	$54.60
Purchase #2	$229.25	9.216%	$250.3777	$250.38	$250.40	$250.40
Purchase #3	$59.57	5.467%	$62.8267	$62.83	$62.85	$62.80
Purchase #4	$204.87	8.478%	$222.2389	$222.24	$222.25	$222.20
Purchase #5	$39.54	12.508%	$44.4857	$44.49	$44.50	$44.50
Purchase #6	$146.81	4.443%	$153.3328	$153.33	$153.35	$153.30
Purchase #7	$205.91	10.369%	$227.2608	$227.26	$227.25	$227.30
7 purchase totals =	$935.51		$1,015.0991	$1,015.11	$1,015.20	$1,015.10