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	$136.59	6.422%	$145.3618	$145.36	$145.35	$145.40
Purchase #2	$181.86	9.254%	$198.6893	$198.69	$198.70	$198.70
Purchase #3	$19.39	13.565%	$22.0203	$22.02	$22.00	$22.00
Purchase #4	$233.74	6.635%	$249.2486	$249.25	$249.25	$249.20
Purchase #5	$241.90	13.870%	$275.4515	$275.45	$275.45	$275.50
Purchase #6	$18.51	7.824%	$19.9582	$19.96	$19.95	$20.00
Purchase #7	$61.30	10.248%	$67.582	$67.58	$67.60	$67.60
7 purchase totals =	$893.29		$978.3117	$978.31	$978.30	$978.40