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	$50.89	13.346%	$57.6818	$57.68	$57.70	$57.70
Purchase #2	$120.97	3.372%	$125.0491	$125.05	$125.05	$125.00
Purchase #3	$205.81	13.372%	$233.3309	$233.33	$233.35	$233.30
Purchase #4	$123.45	9.234%	$134.8494	$134.85	$134.85	$134.80
Purchase #5	$35.41	5.811%	$37.4677	$37.47	$37.45	$37.50
Purchase #6	$77.51	7.245%	$83.1256	$83.13	$83.15	$83.10
Purchase #7	$187.88	6.495%	$200.0828	$200.08	$200.10	$200.10
7 purchase totals =	$801.92		$871.5873	$871.59	$871.65	$871.50