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	$160.44	6.727%	$171.2328	$171.23	$171.25	$171.20
Purchase #2	$236.51	5.602%	$249.7593	$249.76	$249.75	$249.80
Purchase #3	$148.60	11.825%	$166.172	$166.17	$166.15	$166.20
Purchase #4	$17.53	11.725%	$19.5854	$19.59	$19.60	$19.60
Purchase #5	$113.42	5.376%	$119.5175	$119.52	$119.50	$119.50
Purchase #6	$191.85	10.824%	$212.6158	$212.62	$212.60	$212.60
Purchase #7	$75.44	9.397%	$82.5291	$82.53	$82.55	$82.50
7 purchase totals =	$943.79		$1,021.4119	$1,021.42	$1,021.40	$1,021.40