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	$243.85	12.216%	$273.6387	$273.64	$273.65	$273.60
Purchase #2	$127.60	8.484%	$138.4256	$138.43	$138.45	$138.40
Purchase #3	$99.56	9.472%	$108.9903	$108.99	$109.00	$109.00
Purchase #4	$81.61	10.453%	$90.1407	$90.14	$90.15	$90.10
Purchase #5	$183.63	9.356%	$200.8104	$200.81	$200.80	$200.80
Purchase #6	$188.61	3.555%	$195.3151	$195.32	$195.30	$195.30
Purchase #7	$188.65	12.658%	$212.5293	$212.53	$212.55	$212.50
7 purchase totals =	$1,113.51		$1,219.8501	$1,219.86	$1,219.90	$1,219.70