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	$81.60	10.696%	$90.3279	$90.33	$90.35	$90.30
Purchase #2	$212.42	12.733%	$239.4674	$239.47	$239.45	$239.50
Purchase #3	$250.98	10.165%	$276.4921	$276.49	$276.50	$276.50
Purchase #4	$61.36	8.109%	$66.3357	$66.34	$66.35	$66.30
Purchase #5	$243.90	10.686%	$269.9632	$269.96	$269.95	$270.00
Purchase #6	$30.78	4.481%	$32.1593	$32.16	$32.15	$32.20
Purchase #7	$118.76	6.109%	$126.015	$126.02	$126.00	$126.00
7 purchase totals =	$999.80		$1,100.7606	$1,100.77	$1,100.75	$1,100.80