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	$21.32	4.174%	$22.2099	$22.21	$22.20	$22.20
Purchase #2	$89.43	3.688%	$92.7282	$92.73	$92.75	$92.70
Purchase #3	$66.56	8.658%	$72.3228	$72.32	$72.30	$72.30
Purchase #4	$32.83	4.195%	$34.2072	$34.21	$34.20	$34.20
Purchase #5	$134.40	11.678%	$150.0952	$150.10	$150.10	$150.10
Purchase #6	$80.51	11.271%	$89.5843	$89.58	$89.60	$89.60
Purchase #7	$136.93	13.737%	$155.7401	$155.74	$155.75	$155.70
7 purchase totals =	$561.98		$616.8877	$616.89	$616.90	$616.80