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	$94.33	9.806%	$103.58	$103.58	$103.60	$103.60
Purchase #2	$28.36	7.870%	$30.5919	$30.59	$30.60	$30.60
Purchase #3	$125.52	11.501%	$139.9561	$139.96	$139.95	$140.00
Purchase #4	$33.69	10.684%	$37.2894	$37.29	$37.30	$37.30
Purchase #5	$21.47	6.827%	$22.9358	$22.94	$22.95	$22.90
Purchase #6	$100.30	8.658%	$108.984	$108.98	$109.00	$109.00
Purchase #7	$146.44	13.397%	$166.0586	$166.06	$166.05	$166.10
7 purchase totals =	$550.11		$609.3958	$609.40	$609.45	$609.50