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	$98.45	7.634%	$105.9657	$105.97	$105.95	$106.00
Purchase #2	$79.79	3.210%	$82.3513	$82.35	$82.35	$82.40
Purchase #3	$244.98	12.697%	$276.0851	$276.09	$276.10	$276.10
Purchase #4	$86.41	5.163%	$90.8713	$90.87	$90.85	$90.90
Purchase #5	$39.27	13.316%	$44.4992	$44.50	$44.50	$44.50
Purchase #6	$216.48	11.118%	$240.5482	$240.55	$240.55	$240.50
Purchase #7	$68.64	6.267%	$72.9417	$72.94	$72.95	$72.90
7 purchase totals =	$834.02		$913.2625	$913.27	$913.25	$913.30