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	$37.88	7.795%	$40.8327	$40.83	$40.85	$40.80
Purchase #2	$204.47	5.332%	$215.3723	$215.37	$215.35	$215.40
Purchase #3	$135.82	12.390%	$152.6481	$152.65	$152.65	$152.60
Purchase #4	$212.53	12.341%	$238.7583	$238.76	$238.75	$238.80
Purchase #5	$120.52	9.799%	$132.3298	$132.33	$132.35	$132.30
Purchase #6	$71.51	4.213%	$74.5227	$74.52	$74.50	$74.50
Purchase #7	$47.83	12.180%	$53.6557	$53.66	$53.65	$53.70
7 purchase totals =	$830.56		$908.1196	$908.12	$908.10	$908.10