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	$30.78	3.593%	$31.8859	$31.89	$31.90	$31.90
Purchase #2	$61.62	5.202%	$64.8255	$64.83	$64.85	$64.80
Purchase #3	$170.62	5.668%	$180.2907	$180.29	$180.30	$180.30
Purchase #4	$41.27	4.336%	$43.0595	$43.06	$43.05	$43.10
Purchase #5	$49.60	6.167%	$52.6588	$52.66	$52.65	$52.70
Purchase #6	$100.29	3.659%	$103.9596	$103.96	$103.95	$104.00
Purchase #7	$64.58	3.803%	$67.036	$67.04	$67.05	$67.00
7 purchase totals =	$518.76		$543.7160	$543.73	$543.75	$543.80