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	$152.50	11.448%	$169.9582	$169.96	$169.95	$170.00
Purchase #2	$133.72	13.277%	$151.474	$151.47	$151.45	$151.50
Purchase #3	$219.63	7.427%	$235.9419	$235.94	$235.95	$235.90
Purchase #4	$18.79	7.446%	$20.1891	$20.19	$20.20	$20.20
Purchase #5	$56.53	5.450%	$59.6109	$59.61	$59.60	$59.60
Purchase #6	$35.34	9.726%	$38.7772	$38.78	$38.80	$38.80
Purchase #7	$180.80	6.690%	$192.8955	$192.90	$192.90	$192.90
7 purchase totals =	$797.31		$868.8468	$868.85	$868.85	$868.90