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	$198.26	10.169%	$218.4211	$218.42	$218.40	$218.40
Purchase #2	$117.59	11.610%	$131.2422	$131.24	$131.25	$131.20
Purchase #3	$199.81	10.764%	$221.3175	$221.32	$221.30	$221.30
Purchase #4	$58.98	12.730%	$66.4882	$66.49	$66.50	$66.50
Purchase #5	$176.71	12.829%	$199.3801	$199.38	$199.40	$199.40
Purchase #6	$132.38	13.501%	$150.2526	$150.25	$150.25	$150.30
Purchase #7	$6.83	10.392%	$7.5398	$7.54	$7.55	$7.50
7 purchase totals =	$890.56		$994.6415	$994.64	$994.65	$994.60