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	$183.69	11.385%	$204.6031	$204.60	$204.60	$204.60
Purchase #2	$93.83	6.511%	$99.9393	$99.94	$99.95	$99.90
Purchase #3	$89.76	10.799%	$99.4532	$99.45	$99.45	$99.50
Purchase #4	$8.51	7.528%	$9.1506	$9.15	$9.15	$9.20
Purchase #5	$86.29	4.497%	$90.1705	$90.17	$90.15	$90.20
Purchase #6	$39.45	3.507%	$40.8335	$40.83	$40.85	$40.80
Purchase #7	$112.28	6.514%	$119.5939	$119.59	$119.60	$119.60
7 purchase totals =	$613.81		$663.7441	$663.73	$663.75	$663.80