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	$12.28	12.503%	$13.8154	$13.82	$13.80	$13.80
Purchase #2	$40.25	10.557%	$44.4992	$44.50	$44.50	$44.50
Purchase #3	$22.97	10.492%	$25.38	$25.38	$25.40	$25.40
Purchase #4	$89.61	13.178%	$101.4188	$101.42	$101.40	$101.40
Purchase #5	$188.93	12.556%	$212.6521	$212.65	$212.65	$212.70
Purchase #6	$40.84	7.185%	$43.7744	$43.77	$43.75	$43.80
Purchase #7	$57.79	3.659%	$59.9045	$59.90	$59.90	$59.90
7 purchase totals =	$452.67		$501.4444	$501.44	$501.40	$501.50