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	$30.60	10.855%	$33.9216	$33.92	$33.90	$33.90
Purchase #2	$68.53	12.781%	$77.2888	$77.29	$77.30	$77.30
Purchase #3	$136.51	10.751%	$151.1862	$151.19	$151.20	$151.20
Purchase #4	$239.77	10.753%	$265.5525	$265.55	$265.55	$265.60
Purchase #5	$134.29	13.129%	$151.9209	$151.92	$151.90	$151.90
Purchase #6	$96.84	3.857%	$100.5751	$100.58	$100.60	$100.60
Purchase #7	$209.78	6.114%	$222.6059	$222.61	$222.60	$222.60
7 purchase totals =	$916.32		$1,003.0510	$1,003.06	$1,003.05	$1,003.10