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	$18.61	6.449%	$19.8102	$19.81	$19.80	$19.80
Purchase #2	$72.86	7.477%	$78.3077	$78.31	$78.30	$78.30
Purchase #3	$222.94	13.618%	$253.3	$253.30	$253.30	$253.30
Purchase #4	$223.70	4.437%	$233.6256	$233.63	$233.65	$233.60
Purchase #5	$79.93	7.667%	$86.0582	$86.06	$86.05	$86.10
Purchase #6	$212.47	3.784%	$220.5099	$220.51	$220.50	$220.50
Purchase #7	$106.82	5.391%	$112.5787	$112.58	$112.60	$112.60
7 purchase totals =	$937.33		$1,004.1903	$1,004.20	$1,004.20	$1,004.20