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	$58.64	13.723%	$66.6872	$66.69	$66.70	$66.70
Purchase #2	$134.57	7.474%	$144.6278	$144.63	$144.65	$144.60
Purchase #3	$200.81	7.404%	$215.678	$215.68	$215.70	$215.70
Purchase #4	$90.27	6.497%	$96.1348	$96.13	$96.15	$96.10
Purchase #5	$20.30	4.868%	$21.2882	$21.29	$21.30	$21.30
Purchase #6	$45.92	4.208%	$47.8523	$47.85	$47.85	$47.90
Purchase #7	$86.35	12.160%	$96.8502	$96.85	$96.85	$96.90
7 purchase totals =	$636.86		$689.1185	$689.12	$689.20	$689.20