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	$156.62	6.314%	$166.509	$166.51	$166.50	$166.50
Purchase #2	$51.38	6.560%	$54.7505	$54.75	$54.75	$54.80
Purchase #3	$127.62	12.842%	$144.009	$144.01	$144.00	$144.00
Purchase #4	$163.59	12.771%	$184.4821	$184.48	$184.50	$184.50
Purchase #5	$91.35	10.729%	$101.1509	$101.15	$101.15	$101.20
Purchase #6	$136.93	12.691%	$154.3078	$154.31	$154.30	$154.30
Purchase #7	$119.67	9.237%	$130.7239	$130.72	$130.70	$130.70
7 purchase totals =	$847.16		$935.9332	$935.93	$935.90	$936.00