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	$105.79	3.842%	$109.8545	$109.85	$109.85	$109.90
Purchase #2	$122.39	4.602%	$128.0224	$128.02	$128.00	$128.00
Purchase #3	$30.53	6.673%	$32.5673	$32.57	$32.55	$32.60
Purchase #4	$199.92	8.611%	$217.1351	$217.14	$217.15	$217.10
Purchase #5	$61.38	6.259%	$65.2218	$65.22	$65.20	$65.20
Purchase #6	$142.39	9.249%	$155.5597	$155.56	$155.55	$155.60
Purchase #7	$95.76	13.364%	$108.5574	$108.56	$108.55	$108.60
7 purchase totals =	$758.16		$816.9182	$816.92	$816.85	$817.00