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	$69.97	4.169%	$72.887	$72.89	$72.90	$72.90
Purchase #2	$211.55	7.581%	$227.5876	$227.59	$227.60	$227.60
Purchase #3	$44.84	4.464%	$46.8417	$46.84	$46.85	$46.80
Purchase #4	$39.79	8.693%	$43.2489	$43.25	$43.25	$43.20
Purchase #5	$120.43	6.806%	$128.6265	$128.63	$128.65	$128.60
Purchase #6	$85.77	7.785%	$92.4472	$92.45	$92.45	$92.40
Purchase #7	$40.57	4.649%	$42.4561	$42.46	$42.45	$42.50
7 purchase totals =	$612.92		$654.0950	$654.11	$654.15	$654.00