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	$79.95	7.312%	$85.7959	$85.80	$85.80	$85.80
Purchase #2	$191.50	4.651%	$200.4067	$200.41	$200.40	$200.40
Purchase #3	$154.25	9.809%	$169.3804	$169.38	$169.40	$169.40
Purchase #4	$148.41	5.112%	$155.9967	$156.00	$156.00	$156.00
Purchase #5	$169.85	6.873%	$181.5238	$181.52	$181.50	$181.50
Purchase #6	$133.42	12.547%	$150.1602	$150.16	$150.15	$150.20
Purchase #7	$34.59	7.263%	$37.1023	$37.10	$37.10	$37.10
7 purchase totals =	$911.97		$980.3660	$980.37	$980.35	$980.40