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	$9.93	6.127%	$10.5384	$10.54	$10.55	$10.50
Purchase #2	$125.89	11.277%	$140.0866	$140.09	$140.10	$140.10
Purchase #3	$166.98	8.665%	$181.4488	$181.45	$181.45	$181.40
Purchase #4	$59.49	3.633%	$61.6513	$61.65	$61.65	$61.70
Purchase #5	$103.80	5.762%	$109.781	$109.78	$109.80	$109.80
Purchase #6	$65.83	7.846%	$70.995	$71.00	$71.00	$71.00
Purchase #7	$83.47	8.805%	$90.8195	$90.82	$90.80	$90.80
7 purchase totals =	$615.39		$665.3206	$665.33	$665.35	$665.30