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	$219.65	6.378%	$233.6593	$233.66	$233.65	$233.70
Purchase #2	$81.82	10.454%	$90.3735	$90.37	$90.35	$90.40
Purchase #3	$96.80	7.762%	$104.3136	$104.31	$104.30	$104.30
Purchase #4	$80.75	10.407%	$89.1537	$89.15	$89.15	$89.20
Purchase #5	$60.99	12.467%	$68.5936	$68.59	$68.60	$68.60
Purchase #6	$58.27	6.270%	$61.9235	$61.92	$61.90	$61.90
Purchase #7	$170.90	8.634%	$185.6555	$185.66	$185.65	$185.70
7 purchase totals =	$769.18		$833.6727	$833.66	$833.60	$833.80