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	$239.31	13.164%	$270.8128	$270.81	$270.80	$270.80
Purchase #2	$156.94	7.231%	$168.2883	$168.29	$168.30	$168.30
Purchase #3	$179.57	11.466%	$200.1595	$200.16	$200.15	$200.20
Purchase #4	$124.77	6.645%	$133.061	$133.06	$133.05	$133.10
Purchase #5	$112.28	5.297%	$118.2275	$118.23	$118.25	$118.20
Purchase #6	$84.52	9.481%	$92.5333	$92.53	$92.55	$92.50
Purchase #7	$115.88	5.582%	$122.3484	$122.35	$122.35	$122.30
7 purchase totals =	$1,013.27		$1,105.4308	$1,105.43	$1,105.45	$1,105.40