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	$249.96	6.205%	$265.47	$265.47	$265.45	$265.50
Purchase #2	$117.45	10.216%	$129.4487	$129.45	$129.45	$129.40
Purchase #3	$181.80	11.405%	$202.5343	$202.53	$202.55	$202.50
Purchase #4	$166.35	7.571%	$178.9444	$178.94	$178.95	$178.90
Purchase #5	$46.73	12.814%	$52.718	$52.72	$52.70	$52.70
Purchase #6	$117.49	9.233%	$128.3379	$128.34	$128.35	$128.30
Purchase #7	$51.93	13.731%	$59.0605	$59.06	$59.05	$59.10
7 purchase totals =	$931.71		$1,016.5138	$1,016.51	$1,016.50	$1,016.40