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	$61.30	6.427%	$65.2398	$65.24	$65.25	$65.20
Purchase #2	$220.59	3.707%	$228.7673	$228.77	$228.75	$228.80
Purchase #3	$172.45	5.603%	$182.1124	$182.11	$182.10	$182.10
Purchase #4	$36.76	12.748%	$41.4462	$41.45	$41.45	$41.40
Purchase #5	$41.33	9.417%	$45.222	$45.22	$45.20	$45.20
Purchase #6	$7.33	8.825%	$7.9769	$7.98	$8.00	$8.00
Purchase #7	$50.47	13.616%	$57.342	$57.34	$57.35	$57.30
7 purchase totals =	$590.23		$628.1066	$628.11	$628.10	$628.00