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	$24.54	13.589%	$27.8747	$27.87	$27.85	$27.90
Purchase #2	$136.90	13.868%	$155.8853	$155.89	$155.90	$155.90
Purchase #3	$244.90	10.108%	$269.6545	$269.65	$269.65	$269.70
Purchase #4	$41.30	12.680%	$46.5368	$46.54	$46.55	$46.50
Purchase #5	$211.67	3.657%	$219.4108	$219.41	$219.40	$219.40
Purchase #6	$82.34	13.341%	$93.325	$93.33	$93.35	$93.30
Purchase #7	$122.85	11.546%	$137.0343	$137.03	$137.05	$137.00
7 purchase totals =	$864.50		$949.7214	$949.72	$949.75	$949.70