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	$93.57	13.154%	$105.8782	$105.88	$105.90	$105.90
Purchase #2	$36.33	4.487%	$37.9601	$37.96	$37.95	$38.00
Purchase #3	$180.28	13.827%	$205.2073	$205.21	$205.20	$205.20
Purchase #4	$41.45	7.690%	$44.6375	$44.64	$44.65	$44.60
Purchase #5	$97.94	6.548%	$104.3531	$104.35	$104.35	$104.40
Purchase #6	$96.98	12.754%	$109.3488	$109.35	$109.35	$109.30
Purchase #7	$75.50	10.116%	$83.1376	$83.14	$83.15	$83.10
7 purchase totals =	$622.05		$690.5226	$690.53	$690.55	$690.50