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	$64.76	4.258%	$67.5175	$67.52	$67.50	$67.50
Purchase #2	$222.76	10.272%	$245.6419	$245.64	$245.65	$245.60
Purchase #3	$51.40	3.458%	$53.1774	$53.18	$53.20	$53.20
Purchase #4	$143.37	8.641%	$155.7586	$155.76	$155.75	$155.80
Purchase #5	$124.50	4.830%	$130.5134	$130.51	$130.50	$130.50
Purchase #6	$96.44	8.396%	$104.5371	$104.54	$104.55	$104.50
Purchase #7	$99.78	12.200%	$111.9532	$111.95	$111.95	$112.00
7 purchase totals =	$803.01		$869.0991	$869.10	$869.10	$869.10