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	$76.71	9.449%	$83.9583	$83.96	$83.95	$84.00
Purchase #2	$60.64	7.548%	$65.2171	$65.22	$65.20	$65.20
Purchase #3	$122.29	13.277%	$138.5264	$138.53	$138.55	$138.50
Purchase #4	$244.58	13.526%	$277.6619	$277.66	$277.65	$277.70
Purchase #5	$235.71	13.438%	$267.3847	$267.38	$267.40	$267.40
Purchase #6	$57.31	4.528%	$59.905	$59.91	$59.90	$59.90
Purchase #7	$85.81	5.815%	$90.7999	$90.80	$90.80	$90.80
7 purchase totals =	$883.05		$983.4533	$983.46	$983.45	$983.50