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	$16.61	8.483%	$18.019	$18.02	$18.00	$18.00
Purchase #2	$225.94	12.345%	$253.8323	$253.83	$253.85	$253.80
Purchase #3	$106.85	12.131%	$119.812	$119.81	$119.80	$119.80
Purchase #4	$158.83	8.375%	$172.132	$172.13	$172.15	$172.10
Purchase #5	$25.53	9.351%	$27.9173	$27.92	$27.90	$27.90
Purchase #6	$99.49	3.533%	$103.005	$103.01	$103.00	$103.00
Purchase #7	$60.80	11.230%	$67.6278	$67.63	$67.65	$67.60
7 purchase totals =	$694.05		$762.3454	$762.35	$762.35	$762.20