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	$21.84	12.703%	$24.6143	$24.61	$24.60	$24.60
Purchase #2	$92.35	11.808%	$103.2547	$103.25	$103.25	$103.30
Purchase #3	$66.38	8.703%	$72.1571	$72.16	$72.15	$72.20
Purchase #4	$221.67	13.155%	$250.8307	$250.83	$250.85	$250.80
Purchase #5	$126.96	3.473%	$131.3693	$131.37	$131.35	$131.40
Purchase #6	$173.58	12.108%	$194.5971	$194.60	$194.60	$194.60
Purchase #7	$57.74	4.250%	$60.194	$60.19	$60.20	$60.20
7 purchase totals =	$760.52		$837.0172	$837.01	$837.00	$837.10