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	$141.71	5.453%	$149.4374	$149.44	$149.45	$149.40
Purchase #2	$125.40	5.246%	$131.9785	$131.98	$132.00	$132.00
Purchase #3	$202.27	10.197%	$222.8955	$222.90	$222.90	$222.90
Purchase #4	$114.51	7.688%	$123.3135	$123.31	$123.30	$123.30
Purchase #5	$143.49	4.597%	$150.0862	$150.09	$150.10	$150.10
Purchase #6	$90.46	5.778%	$95.6868	$95.69	$95.70	$95.70
Purchase #7	$43.71	5.811%	$46.25	$46.25	$46.25	$46.30
7 purchase totals =	$861.55		$919.6479	$919.66	$919.70	$919.70