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	$86.86	13.371%	$98.4741	$98.47	$98.45	$98.50
Purchase #2	$72.30	10.523%	$79.9081	$79.91	$79.90	$79.90
Purchase #3	$160.32	8.439%	$173.8494	$173.85	$173.85	$173.80
Purchase #4	$194.61	11.580%	$217.1458	$217.15	$217.15	$217.10
Purchase #5	$86.77	12.378%	$97.5104	$97.51	$97.50	$97.50
Purchase #6	$36.30	12.464%	$40.8244	$40.82	$40.80	$40.80
Purchase #7	$130.47	7.702%	$140.5188	$140.52	$140.50	$140.50
7 purchase totals =	$767.63		$848.2310	$848.23	$848.15	$848.10