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	$6.92	9.730%	$7.5933	$7.59	$7.60	$7.60
Purchase #2	$101.52	11.414%	$113.1075	$113.11	$113.10	$113.10
Purchase #3	$242.85	9.269%	$265.3598	$265.36	$265.35	$265.40
Purchase #4	$114.76	13.392%	$130.1287	$130.13	$130.15	$130.10
Purchase #5	$92.43	3.431%	$95.6013	$95.60	$95.60	$95.60
Purchase #6	$246.35	7.356%	$264.4715	$264.47	$264.45	$264.50
Purchase #7	$197.89	13.536%	$224.6764	$224.68	$224.70	$224.70
7 purchase totals =	$1,002.72		$1,100.9385	$1,100.94	$1,100.95	$1,101.00