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	$133.83	8.240%	$144.8576	$144.86	$144.85	$144.90
Purchase #2	$224.28	7.403%	$240.8834	$240.88	$240.90	$240.90
Purchase #3	$237.33	11.145%	$263.7804	$263.78	$263.80	$263.80
Purchase #4	$40.95	10.647%	$45.3099	$45.31	$45.30	$45.30
Purchase #5	$60.25	7.527%	$64.785	$64.79	$64.80	$64.80
Purchase #6	$37.28	9.434%	$40.797	$40.80	$40.80	$40.80
Purchase #7	$38.37	9.341%	$41.9541	$41.95	$41.95	$42.00
7 purchase totals =	$772.29		$842.3674	$842.37	$842.40	$842.50