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	$106.48	10.766%	$117.9436	$117.94	$117.95	$117.90
Purchase #2	$207.40	12.579%	$233.4888	$233.49	$233.50	$233.50
Purchase #3	$123.90	12.312%	$139.1546	$139.15	$139.15	$139.20
Purchase #4	$128.65	5.854%	$136.1812	$136.18	$136.20	$136.20
Purchase #5	$232.37	13.464%	$263.6563	$263.66	$263.65	$263.70
Purchase #6	$82.27	10.180%	$90.6451	$90.65	$90.65	$90.60
Purchase #7	$180.71	10.840%	$200.299	$200.30	$200.30	$200.30
7 purchase totals =	$1,061.78		$1,181.3686	$1,181.37	$1,181.40	$1,181.40