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	$104.45	3.494%	$108.0995	$108.10	$108.10	$108.10
Purchase #2	$98.74	5.230%	$103.9041	$103.90	$103.90	$103.90
Purchase #3	$168.50	11.128%	$187.2507	$187.25	$187.25	$187.30
Purchase #4	$147.28	8.119%	$159.2377	$159.24	$159.25	$159.20
Purchase #5	$53.66	3.299%	$55.4302	$55.43	$55.45	$55.40
Purchase #6	$17.75	4.182%	$18.4923	$18.49	$18.50	$18.50
Purchase #7	$186.46	5.454%	$196.6295	$196.63	$196.65	$196.60
7 purchase totals =	$776.84		$829.0440	$829.04	$829.10	$829.00