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	$230.34	11.873%	$257.6883	$257.69	$257.70	$257.70
Purchase #2	$78.61	9.361%	$85.9687	$85.97	$85.95	$86.00
Purchase #3	$26.33	13.438%	$29.8682	$29.87	$29.85	$29.90
Purchase #4	$115.58	13.449%	$131.1244	$131.12	$131.10	$131.10
Purchase #5	$83.42	3.217%	$86.1036	$86.10	$86.10	$86.10
Purchase #6	$119.25	3.481%	$123.4011	$123.40	$123.40	$123.40
Purchase #7	$119.86	13.578%	$136.1346	$136.13	$136.15	$136.10
7 purchase totals =	$773.39		$850.2889	$850.28	$850.25	$850.30