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	$103.95	4.515%	$108.6433	$108.64	$108.65	$108.60
Purchase #2	$213.93	3.574%	$221.5759	$221.58	$221.60	$221.60
Purchase #3	$72.87	8.283%	$78.9058	$78.91	$78.90	$78.90
Purchase #4	$97.63	12.487%	$109.8211	$109.82	$109.80	$109.80
Purchase #5	$158.30	5.430%	$166.8957	$166.90	$166.90	$166.90
Purchase #6	$21.42	6.463%	$22.8044	$22.80	$22.80	$22.80
Purchase #7	$41.91	8.132%	$45.3181	$45.32	$45.30	$45.30
7 purchase totals =	$710.01		$753.9643	$753.97	$753.95	$753.90