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	$21.72	7.103%	$23.2628	$23.26	$23.25	$23.30
Purchase #2	$206.41	12.790%	$232.8098	$232.81	$232.80	$232.80
Purchase #3	$106.70	4.586%	$111.5933	$111.59	$111.60	$111.60
Purchase #4	$212.77	4.287%	$221.8914	$221.89	$221.90	$221.90
Purchase #5	$137.94	10.404%	$152.2913	$152.29	$152.30	$152.30
Purchase #6	$188.55	4.275%	$196.6105	$196.61	$196.60	$196.60
Purchase #7	$47.59	5.630%	$50.2693	$50.27	$50.25	$50.30
7 purchase totals =	$921.68		$988.7284	$988.72	$988.70	$988.80