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	$47.78	13.607%	$54.2814	$54.28	$54.30	$54.30
Purchase #2	$47.44	9.160%	$51.7855	$51.79	$51.80	$51.80
Purchase #3	$125.57	4.670%	$131.4341	$131.43	$131.45	$131.40
Purchase #4	$180.51	13.440%	$204.7705	$204.77	$204.75	$204.80
Purchase #5	$106.76	8.760%	$116.1122	$116.11	$116.10	$116.10
Purchase #6	$128.82	13.681%	$146.4439	$146.44	$146.45	$146.40
Purchase #7	$86.28	4.749%	$90.3774	$90.38	$90.40	$90.40
7 purchase totals =	$723.16		$795.2050	$795.20	$795.25	$795.20