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	$48.67	12.781%	$54.8905	$54.89	$54.90	$54.90
Purchase #2	$79.43	13.823%	$90.4096	$90.41	$90.40	$90.40
Purchase #3	$69.25	13.653%	$78.7047	$78.70	$78.70	$78.70
Purchase #4	$175.87	10.153%	$193.7261	$193.73	$193.75	$193.70
Purchase #5	$32.64	11.849%	$36.5075	$36.51	$36.50	$36.50
Purchase #6	$174.73	10.763%	$193.5362	$193.54	$193.55	$193.50
Purchase #7	$53.96	13.707%	$61.3563	$61.36	$61.35	$61.40
7 purchase totals =	$634.55		$709.1309	$709.14	$709.15	$709.10