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	$183.60	10.583%	$203.0304	$203.03	$203.05	$203.00
Purchase #2	$24.57	13.624%	$27.9174	$27.92	$27.90	$27.90
Purchase #3	$40.50	11.132%	$45.0085	$45.01	$45.00	$45.00
Purchase #4	$177.79	4.418%	$185.6448	$185.64	$185.65	$185.60
Purchase #5	$66.78	5.285%	$70.3093	$70.31	$70.30	$70.30
Purchase #6	$178.30	6.507%	$189.902	$189.90	$189.90	$189.90
Purchase #7	$85.28	6.155%	$90.529	$90.53	$90.55	$90.50
7 purchase totals =	$756.82		$812.3414	$812.34	$812.35	$812.20