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	$204.86	8.140%	$221.5356	$221.54	$221.55	$221.50
Purchase #2	$159.54	13.820%	$181.5884	$181.59	$181.60	$181.60
Purchase #3	$47.39	12.740%	$53.4275	$53.43	$53.45	$53.40
Purchase #4	$31.97	4.715%	$33.4774	$33.48	$33.50	$33.50
Purchase #5	$68.52	13.664%	$77.8826	$77.88	$77.90	$77.90
Purchase #6	$214.31	4.812%	$224.6226	$224.62	$224.60	$224.60
Purchase #7	$70.70	12.439%	$79.4944	$79.49	$79.50	$79.50
7 purchase totals =	$797.29		$872.0285	$872.03	$872.10	$872.00