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	$101.51	3.214%	$104.7725	$104.77	$104.75	$104.80
Purchase #2	$55.55	13.249%	$62.9098	$62.91	$62.90	$62.90
Purchase #3	$234.26	4.280%	$244.2863	$244.29	$244.30	$244.30
Purchase #4	$75.63	6.535%	$80.5724	$80.57	$80.55	$80.60
Purchase #5	$168.58	13.198%	$190.8292	$190.83	$190.85	$190.80
Purchase #6	$132.88	7.491%	$142.834	$142.83	$142.85	$142.80
Purchase #7	$88.41	11.532%	$98.6054	$98.61	$98.60	$98.60
7 purchase totals =	$856.82		$924.8096	$924.81	$924.80	$924.80