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	$227.72	6.431%	$242.3647	$242.36	$242.35	$242.40
Purchase #2	$161.66	6.324%	$171.8834	$171.88	$171.90	$171.90
Purchase #3	$154.72	6.234%	$164.3652	$164.37	$164.35	$164.40
Purchase #4	$8.94	9.661%	$9.8037	$9.80	$9.80	$9.80
Purchase #5	$58.60	6.821%	$62.5971	$62.60	$62.60	$62.60
Purchase #6	$51.29	12.721%	$57.8146	$57.81	$57.80	$57.80
Purchase #7	$133.46	13.144%	$151.002	$151.00	$151.00	$151.00
7 purchase totals =	$796.39		$859.8307	$859.82	$859.80	$859.90