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	$12.35	5.722%	$13.0567	$13.06	$13.05	$13.10
Purchase #2	$54.68	10.407%	$60.3705	$60.37	$60.35	$60.40
Purchase #3	$36.85	12.749%	$41.548	$41.55	$41.55	$41.50
Purchase #4	$213.92	12.833%	$241.3724	$241.37	$241.35	$241.40
Purchase #5	$218.72	13.616%	$248.5009	$248.50	$248.50	$248.50
Purchase #6	$82.35	10.372%	$90.8913	$90.89	$90.90	$90.90
Purchase #7	$218.64	5.585%	$230.851	$230.85	$230.85	$230.90
7 purchase totals =	$837.51		$926.5908	$926.59	$926.55	$926.70