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	$64.36	13.284%	$72.9096	$72.91	$72.90	$72.90
Purchase #2	$86.75	4.313%	$90.4915	$90.49	$90.50	$90.50
Purchase #3	$90.47	9.825%	$99.3587	$99.36	$99.35	$99.40
Purchase #4	$88.31	7.324%	$94.7778	$94.78	$94.80	$94.80
Purchase #5	$199.31	5.215%	$209.704	$209.70	$209.70	$209.70
Purchase #6	$30.55	12.274%	$34.2997	$34.30	$34.30	$34.30
Purchase #7	$14.86	13.324%	$16.8399	$16.84	$16.85	$16.80
7 purchase totals =	$574.61		$618.3812	$618.38	$618.40	$618.40