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	$219.32	4.429%	$229.0337	$229.03	$229.05	$229.00
Purchase #2	$105.64	6.488%	$112.4939	$112.49	$112.50	$112.50
Purchase #3	$39.87	4.133%	$41.5178	$41.52	$41.50	$41.50
Purchase #4	$100.71	3.106%	$103.8381	$103.84	$103.85	$103.80
Purchase #5	$90.32	11.521%	$100.7258	$100.73	$100.75	$100.70
Purchase #6	$32.72	4.855%	$34.3086	$34.31	$34.30	$34.30
Purchase #7	$229.89	12.280%	$258.1205	$258.12	$258.10	$258.10
7 purchase totals =	$818.47		$880.0384	$880.04	$880.05	$879.90