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	$53.46	10.257%	$58.9434	$58.94	$58.95	$58.90
Purchase #2	$55.44	11.341%	$61.7275	$61.73	$61.75	$61.70
Purchase #3	$139.63	9.570%	$152.9926	$152.99	$153.00	$153.00
Purchase #4	$18.69	13.781%	$21.2657	$21.27	$21.25	$21.30
Purchase #5	$98.64	13.201%	$111.6615	$111.66	$111.65	$111.70
Purchase #6	$234.51	3.714%	$243.2197	$243.22	$243.20	$243.20
Purchase #7	$172.90	4.793%	$181.1871	$181.19	$181.20	$181.20
7 purchase totals =	$773.27		$830.9975	$831.00	$831.00	$831.00