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	$38.62	9.132%	$42.1468	$42.15	$42.15	$42.10
Purchase #2	$66.44	6.615%	$70.835	$70.84	$70.85	$70.80
Purchase #3	$116.36	3.465%	$120.3919	$120.39	$120.40	$120.40
Purchase #4	$162.81	4.477%	$170.099	$170.10	$170.10	$170.10
Purchase #5	$80.72	11.690%	$90.1562	$90.16	$90.15	$90.20
Purchase #6	$101.67	12.789%	$114.6726	$114.67	$114.65	$114.70
Purchase #7	$178.41	11.314%	$198.5953	$198.60	$198.60	$198.60
7 purchase totals =	$745.03		$806.8968	$806.91	$806.90	$806.90