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	$46.87	4.732%	$49.0879	$49.09	$49.10	$49.10
Purchase #2	$146.77	11.839%	$164.1461	$164.15	$164.15	$164.10
Purchase #3	$134.92	13.736%	$153.4526	$153.45	$153.45	$153.50
Purchase #4	$77.79	5.408%	$81.9969	$82.00	$82.00	$82.00
Purchase #5	$81.51	5.252%	$85.7909	$85.79	$85.80	$85.80
Purchase #6	$73.57	6.787%	$78.5632	$78.56	$78.55	$78.60
Purchase #7	$88.70	12.517%	$99.8026	$99.80	$99.80	$99.80
7 purchase totals =	$650.13		$712.8402	$712.84	$712.85	$712.90