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	$64.86	12.354%	$72.8728	$72.87	$72.85	$72.90
Purchase #2	$249.55	6.562%	$265.9255	$265.93	$265.95	$265.90
Purchase #3	$168.67	4.809%	$176.7813	$176.78	$176.80	$176.80
Purchase #4	$92.58	4.477%	$96.7248	$96.72	$96.70	$96.70
Purchase #5	$135.53	12.600%	$152.6068	$152.61	$152.60	$152.60
Purchase #6	$62.71	6.113%	$66.5435	$66.54	$66.55	$66.50
Purchase #7	$25.42	12.477%	$28.5917	$28.59	$28.60	$28.60
7 purchase totals =	$799.32		$860.0464	$860.04	$860.05	$860.00