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	$229.28	4.421%	$239.4165	$239.42	$239.40	$239.40
Purchase #2	$112.79	5.513%	$119.0081	$119.01	$119.00	$119.00
Purchase #3	$71.83	8.718%	$78.0921	$78.09	$78.10	$78.10
Purchase #4	$77.76	7.776%	$83.8066	$83.81	$83.80	$83.80
Purchase #5	$192.89	5.789%	$204.0564	$204.06	$204.05	$204.10
Purchase #6	$164.27	6.632%	$175.1644	$175.16	$175.15	$175.20
Purchase #7	$28.96	11.282%	$32.2273	$32.23	$32.25	$32.20
7 purchase totals =	$877.78		$931.7714	$931.78	$931.75	$931.80