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	$218.26	9.145%	$238.2199	$238.22	$238.20	$238.20
Purchase #2	$202.48	13.372%	$229.5556	$229.56	$229.55	$229.60
Purchase #3	$174.37	6.170%	$185.1286	$185.13	$185.15	$185.10
Purchase #4	$88.71	12.484%	$99.7846	$99.78	$99.80	$99.80
Purchase #5	$28.75	13.383%	$32.5976	$32.60	$32.60	$32.60
Purchase #6	$109.93	5.537%	$116.0168	$116.02	$116.00	$116.00
Purchase #7	$195.96	12.156%	$219.7809	$219.78	$219.80	$219.80
7 purchase totals =	$1,018.46		$1,121.0840	$1,121.09	$1,121.10	$1,121.10