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	$101.95	10.624%	$112.7812	$112.78	$112.80	$112.80
Purchase #2	$33.47	11.563%	$37.3401	$37.34	$37.35	$37.30
Purchase #3	$46.61	6.118%	$49.4616	$49.46	$49.45	$49.50
Purchase #4	$231.68	10.309%	$255.5639	$255.56	$255.55	$255.60
Purchase #5	$116.92	3.423%	$120.9222	$120.92	$120.90	$120.90
Purchase #6	$21.74	12.429%	$24.4421	$24.44	$24.45	$24.40
Purchase #7	$82.47	5.297%	$86.8384	$86.84	$86.85	$86.80
7 purchase totals =	$634.84		$687.3495	$687.34	$687.35	$687.30