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	$91.83	6.493%	$97.7925	$97.79	$97.80	$97.80
Purchase #2	$221.62	6.622%	$236.2957	$236.30	$236.30	$236.30
Purchase #3	$178.59	10.195%	$196.7973	$196.80	$196.80	$196.80
Purchase #4	$33.44	11.553%	$37.3033	$37.30	$37.30	$37.30
Purchase #5	$93.42	9.412%	$102.2127	$102.21	$102.20	$102.20
Purchase #6	$170.74	11.626%	$190.5902	$190.59	$190.60	$190.60
Purchase #7	$159.50	8.839%	$173.5982	$173.60	$173.60	$173.60
7 purchase totals =	$949.14		$1,034.5899	$1,034.59	$1,034.60	$1,034.60