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	$61.82	12.291%	$69.4183	$69.42	$69.40	$69.40
Purchase #2	$122.41	12.615%	$137.852	$137.85	$137.85	$137.90
Purchase #3	$36.28	6.207%	$38.5319	$38.53	$38.55	$38.50
Purchase #4	$190.46	3.139%	$196.4385	$196.44	$196.45	$196.40
Purchase #5	$223.39	13.424%	$253.3779	$253.38	$253.40	$253.40
Purchase #6	$250.41	3.715%	$259.7127	$259.71	$259.70	$259.70
Purchase #7	$44.45	13.385%	$50.3996	$50.40	$50.40	$50.40
7 purchase totals =	$929.22		$1,005.7309	$1,005.73	$1,005.75	$1,005.70