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	$93.90	5.775%	$99.3227	$99.32	$99.30	$99.30
Purchase #2	$139.76	4.435%	$145.9584	$145.96	$145.95	$146.00
Purchase #3	$27.62	6.605%	$29.4443	$29.44	$29.45	$29.40
Purchase #4	$76.48	13.656%	$86.9241	$86.92	$86.90	$86.90
Purchase #5	$192.83	8.311%	$208.8561	$208.86	$208.85	$208.90
Purchase #6	$229.94	7.147%	$246.3738	$246.37	$246.35	$246.40
Purchase #7	$26.33	4.596%	$27.5401	$27.54	$27.55	$27.50
7 purchase totals =	$786.86		$844.4195	$844.41	$844.35	$844.40