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	$100.73	4.356%	$105.1178	$105.12	$105.10	$105.10
Purchase #2	$164.39	4.272%	$171.4127	$171.41	$171.40	$171.40
Purchase #3	$72.30	10.406%	$79.8235	$79.82	$79.80	$79.80
Purchase #4	$63.80	13.655%	$72.5119	$72.51	$72.50	$72.50
Purchase #5	$7.28	13.711%	$8.2782	$8.28	$8.30	$8.30
Purchase #6	$239.43	5.456%	$252.4933	$252.49	$252.50	$252.50
Purchase #7	$146.74	5.124%	$154.259	$154.26	$154.25	$154.30
7 purchase totals =	$794.67		$843.8964	$843.89	$843.85	$843.90