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	$38.63	6.377%	$41.0934	$41.09	$41.10	$41.10
Purchase #2	$137.89	10.616%	$152.5284	$152.53	$152.55	$152.50
Purchase #3	$234.89	8.604%	$255.0999	$255.10	$255.10	$255.10
Purchase #4	$96.93	12.809%	$109.3458	$109.35	$109.35	$109.30
Purchase #5	$179.28	7.207%	$192.2007	$192.20	$192.20	$192.20
Purchase #6	$112.97	13.179%	$127.8583	$127.86	$127.85	$127.90
Purchase #7	$66.69	9.433%	$72.9809	$72.98	$73.00	$73.00
7 purchase totals =	$867.28		$951.1074	$951.11	$951.15	$951.10