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	$102.34	10.521%	$113.1072	$113.11	$113.10	$113.10
Purchase #2	$99.40	13.685%	$113.0029	$113.00	$113.00	$113.00
Purchase #3	$140.64	12.790%	$158.6279	$158.63	$158.65	$158.60
Purchase #4	$73.80	11.390%	$82.2058	$82.21	$82.20	$82.20
Purchase #5	$177.98	10.653%	$196.9402	$196.94	$196.95	$196.90
Purchase #6	$39.63	5.361%	$41.7546	$41.75	$41.75	$41.80
Purchase #7	$76.61	4.231%	$79.8514	$79.85	$79.85	$79.90
7 purchase totals =	$710.40		$785.4900	$785.49	$785.50	$785.50