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	$61.77	10.783%	$68.4307	$68.43	$68.45	$68.40
Purchase #2	$57.65	12.358%	$64.7744	$64.77	$64.75	$64.80
Purchase #3	$99.27	9.733%	$108.9319	$108.93	$108.95	$108.90
Purchase #4	$77.38	10.278%	$85.3331	$85.33	$85.35	$85.30
Purchase #5	$35.42	8.846%	$38.5533	$38.55	$38.55	$38.60
Purchase #6	$53.32	8.645%	$57.9295	$57.93	$57.95	$57.90
Purchase #7	$171.82	3.356%	$177.5863	$177.59	$177.60	$177.60
7 purchase totals =	$556.63		$601.5392	$601.53	$601.60	$601.50