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	$7.53	13.798%	$8.569	$8.57	$8.55	$8.60
Purchase #2	$117.64	12.106%	$131.8815	$131.88	$131.90	$131.90
Purchase #3	$98.90	12.675%	$111.4356	$111.44	$111.45	$111.40
Purchase #4	$79.70	13.190%	$90.2124	$90.21	$90.20	$90.20
Purchase #5	$128.89	8.338%	$139.6368	$139.64	$139.65	$139.60
Purchase #6	$36.26	5.716%	$38.3326	$38.33	$38.35	$38.30
Purchase #7	$143.59	6.743%	$153.2723	$153.27	$153.25	$153.30
7 purchase totals =	$612.51		$673.3402	$673.34	$673.35	$673.30