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	$29.47	6.647%	$31.4289	$31.43	$31.45	$31.40
Purchase #2	$184.92	12.683%	$208.3734	$208.37	$208.35	$208.40
Purchase #3	$89.95	13.577%	$102.1625	$102.16	$102.15	$102.20
Purchase #4	$181.96	6.375%	$193.56	$193.56	$193.55	$193.60
Purchase #5	$230.64	12.673%	$259.869	$259.87	$259.85	$259.90
Purchase #6	$85.72	12.580%	$96.5036	$96.50	$96.50	$96.50
Purchase #7	$179.69	9.111%	$196.0616	$196.06	$196.05	$196.10
7 purchase totals =	$982.35		$1,087.9590	$1,087.95	$1,087.90	$1,088.10