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	$185.94	12.841%	$209.8166	$209.82	$209.80	$209.80
Purchase #2	$138.41	11.630%	$154.5071	$154.51	$154.50	$154.50
Purchase #3	$164.77	12.147%	$184.7846	$184.78	$184.80	$184.80
Purchase #4	$215.86	7.411%	$231.8574	$231.86	$231.85	$231.90
Purchase #5	$207.33	7.850%	$223.6054	$223.61	$223.60	$223.60
Purchase #6	$55.63	12.291%	$62.4675	$62.47	$62.45	$62.50
Purchase #7	$118.76	3.665%	$123.1126	$123.11	$123.10	$123.10
7 purchase totals =	$1,086.70		$1,190.1512	$1,190.16	$1,190.10	$1,190.20