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	$77.56	6.615%	$82.6906	$82.69	$82.70	$82.70
Purchase #2	$102.79	11.651%	$114.7661	$114.77	$114.75	$114.80
Purchase #3	$148.78	10.590%	$164.5358	$164.54	$164.55	$164.50
Purchase #4	$59.74	13.145%	$67.5928	$67.59	$67.60	$67.60
Purchase #5	$103.28	11.638%	$115.2997	$115.30	$115.30	$115.30
Purchase #6	$171.65	11.539%	$191.4567	$191.46	$191.45	$191.50
Purchase #7	$20.87	12.840%	$23.5497	$23.55	$23.55	$23.50
7 purchase totals =	$684.67		$759.8914	$759.90	$759.90	$759.90