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	$70.84	4.471%	$74.0073	$74.01	$74.00	$74.00
Purchase #2	$19.91	8.506%	$21.6035	$21.60	$21.60	$21.60
Purchase #3	$107.83	11.189%	$119.8951	$119.90	$119.90	$119.90
Purchase #4	$167.73	13.103%	$189.7077	$189.71	$189.70	$189.70
Purchase #5	$68.28	6.770%	$72.9026	$72.90	$72.90	$72.90
Purchase #6	$130.62	7.476%	$140.3852	$140.39	$140.40	$140.40
Purchase #7	$206.54	7.771%	$222.5902	$222.59	$222.60	$222.60
7 purchase totals =	$771.75		$841.0916	$841.10	$841.10	$841.10