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	$31.78	6.715%	$33.914	$33.91	$33.90	$33.90
Purchase #2	$182.97	4.318%	$190.8706	$190.87	$190.85	$190.90
Purchase #3	$91.26	8.641%	$99.1458	$99.15	$99.15	$99.10
Purchase #4	$208.49	5.316%	$219.5733	$219.57	$219.55	$219.60
Purchase #5	$61.45	9.310%	$67.171	$67.17	$67.15	$67.20
Purchase #6	$196.79	9.346%	$215.182	$215.18	$215.20	$215.20
Purchase #7	$54.89	3.837%	$56.9961	$57.00	$57.00	$57.00
7 purchase totals =	$827.63		$882.8528	$882.85	$882.80	$882.90