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	$59.65	11.106%	$66.2747	$66.27	$66.25	$66.30
Purchase #2	$125.89	13.498%	$142.8826	$142.88	$142.90	$142.90
Purchase #3	$70.58	11.657%	$78.8075	$78.81	$78.80	$78.80
Purchase #4	$82.44	9.394%	$90.1844	$90.18	$90.20	$90.20
Purchase #5	$142.40	6.187%	$151.2103	$151.21	$151.20	$151.20
Purchase #6	$220.87	9.473%	$241.793	$241.79	$241.80	$241.80
Purchase #7	$71.67	10.538%	$79.2226	$79.22	$79.20	$79.20
7 purchase totals =	$773.50		$850.3751	$850.36	$850.35	$850.40