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	$9.33	8.161%	$10.0914	$10.09	$10.10	$10.10
Purchase #2	$188.33	4.515%	$196.8331	$196.83	$196.85	$196.80
Purchase #3	$75.78	13.238%	$85.8118	$85.81	$85.80	$85.80
Purchase #4	$213.62	13.265%	$241.9567	$241.96	$241.95	$242.00
Purchase #5	$56.92	7.536%	$61.2095	$61.21	$61.20	$61.20
Purchase #6	$189.25	12.659%	$213.2072	$213.21	$213.20	$213.20
Purchase #7	$225.91	6.298%	$240.1378	$240.14	$240.15	$240.10
7 purchase totals =	$959.14		$1,049.2475	$1,049.25	$1,049.25	$1,049.20