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	$100.83	3.521%	$104.3802	$104.38	$104.40	$104.40
Purchase #2	$203.54	3.834%	$211.3437	$211.34	$211.35	$211.30
Purchase #3	$116.92	8.743%	$127.1423	$127.14	$127.15	$127.10
Purchase #4	$77.93	5.812%	$82.4593	$82.46	$82.45	$82.50
Purchase #5	$88.82	6.383%	$94.4894	$94.49	$94.50	$94.50
Purchase #6	$166.69	9.736%	$182.9189	$182.92	$182.90	$182.90
Purchase #7	$16.74	8.816%	$18.2158	$18.22	$18.20	$18.20
7 purchase totals =	$771.47		$820.9496	$820.95	$820.95	$820.90