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	$249.32	3.290%	$257.5226	$257.52	$257.50	$257.50
Purchase #2	$91.94	6.682%	$98.0834	$98.08	$98.10	$98.10
Purchase #3	$247.54	13.498%	$280.9529	$280.95	$280.95	$281.00
Purchase #4	$166.27	7.269%	$178.3562	$178.36	$178.35	$178.40
Purchase #5	$219.81	10.768%	$243.4791	$243.48	$243.50	$243.50
Purchase #6	$200.42	4.727%	$209.8939	$209.89	$209.90	$209.90
Purchase #7	$175.95	5.392%	$185.4372	$185.44	$185.45	$185.40
7 purchase totals =	$1,351.25		$1,453.7253	$1,453.72	$1,453.75	$1,453.80