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	$125.39	3.489%	$129.7649	$129.76	$129.75	$129.80
Purchase #2	$134.92	5.197%	$141.9318	$141.93	$141.95	$141.90
Purchase #3	$89.89	10.730%	$99.5352	$99.54	$99.55	$99.50
Purchase #4	$235.37	10.474%	$260.0227	$260.02	$260.00	$260.00
Purchase #5	$120.30	5.852%	$127.34	$127.34	$127.35	$127.30
Purchase #6	$97.93	4.825%	$102.6551	$102.66	$102.65	$102.70
Purchase #7	$72.33	12.791%	$81.5817	$81.58	$81.60	$81.60
7 purchase totals =	$876.13		$942.8314	$942.83	$942.85	$942.80