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	$99.77	6.814%	$106.5683	$106.57	$106.55	$106.60
Purchase #2	$90.33	8.824%	$98.3007	$98.30	$98.30	$98.30
Purchase #3	$83.74	8.580%	$90.9249	$90.92	$90.90	$90.90
Purchase #4	$205.43	7.651%	$221.1474	$221.15	$221.15	$221.10
Purchase #5	$11.93	4.758%	$12.4976	$12.50	$12.50	$12.50
Purchase #6	$217.79	5.800%	$230.4218	$230.42	$230.40	$230.40
Purchase #7	$115.72	7.284%	$124.149	$124.15	$124.15	$124.10
7 purchase totals =	$824.71		$884.0097	$884.01	$883.95	$883.90