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	$17.59	3.346%	$18.1786	$18.18	$18.20	$18.20
Purchase #2	$146.74	13.409%	$166.4164	$166.42	$166.40	$166.40
Purchase #3	$85.25	8.282%	$92.3104	$92.31	$92.30	$92.30
Purchase #4	$95.88	8.339%	$103.8754	$103.88	$103.90	$103.90
Purchase #5	$113.82	4.144%	$118.5367	$118.54	$118.55	$118.50
Purchase #6	$143.54	8.408%	$155.6088	$155.61	$155.60	$155.60
Purchase #7	$98.60	8.418%	$106.9001	$106.90	$106.90	$106.90
7 purchase totals =	$701.42		$761.8264	$761.84	$761.85	$761.80