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	$250.39	11.606%	$279.4503	$279.45	$279.45	$279.50
Purchase #2	$186.56	4.480%	$194.9179	$194.92	$194.90	$194.90
Purchase #3	$196.98	10.702%	$218.0608	$218.06	$218.05	$218.10
Purchase #4	$168.66	13.698%	$191.763	$191.76	$191.75	$191.80
Purchase #5	$7.63	10.392%	$8.4229	$8.42	$8.40	$8.40
Purchase #6	$55.86	9.508%	$61.1712	$61.17	$61.15	$61.20
Purchase #7	$105.95	5.731%	$112.022	$112.02	$112.00	$112.00
7 purchase totals =	$972.03		$1,065.8081	$1,065.80	$1,065.70	$1,065.90