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	$131.40	5.571%	$138.7203	$138.72	$138.70	$138.70
Purchase #2	$221.77	6.644%	$236.5044	$236.50	$236.50	$236.50
Purchase #3	$73.89	9.653%	$81.0226	$81.02	$81.00	$81.00
Purchase #4	$52.41	13.497%	$59.4838	$59.48	$59.50	$59.50
Purchase #5	$41.34	6.310%	$43.9486	$43.95	$43.95	$43.90
Purchase #6	$112.75	13.491%	$127.9611	$127.96	$127.95	$128.00
Purchase #7	$121.47	6.109%	$128.8906	$128.89	$128.90	$128.90
7 purchase totals =	$755.03		$816.5314	$816.52	$816.50	$816.50