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	$5.61	11.471%	$6.2535	$6.25	$6.25	$6.30
Purchase #2	$183.47	4.740%	$192.1665	$192.17	$192.15	$192.20
Purchase #3	$100.34	9.460%	$109.8322	$109.83	$109.85	$109.80
Purchase #4	$85.89	10.834%	$95.1953	$95.20	$95.20	$95.20
Purchase #5	$206.26	7.851%	$222.4535	$222.45	$222.45	$222.50
Purchase #6	$123.92	12.409%	$139.2972	$139.30	$139.30	$139.30
Purchase #7	$6.78	8.431%	$7.3516	$7.35	$7.35	$7.40
7 purchase totals =	$712.27		$772.5498	$772.55	$772.55	$772.70