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	$99.48	13.700%	$113.1088	$113.11	$113.10	$113.10
Purchase #2	$236.70	13.723%	$269.1823	$269.18	$269.20	$269.20
Purchase #3	$205.90	8.455%	$223.3088	$223.31	$223.30	$223.30
Purchase #4	$62.57	7.593%	$67.3209	$67.32	$67.30	$67.30
Purchase #5	$142.79	5.674%	$150.8919	$150.89	$150.90	$150.90
Purchase #6	$37.52	12.264%	$42.1215	$42.12	$42.10	$42.10
Purchase #7	$237.60	6.401%	$252.8088	$252.81	$252.80	$252.80
7 purchase totals =	$1,022.56		$1,118.7430	$1,118.74	$1,118.70	$1,118.70