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	$178.54	3.818%	$185.3567	$185.36	$185.35	$185.40
Purchase #2	$165.53	8.564%	$179.706	$179.71	$179.70	$179.70
Purchase #3	$15.40	13.136%	$17.4229	$17.42	$17.40	$17.40
Purchase #4	$244.97	10.233%	$270.0378	$270.04	$270.05	$270.00
Purchase #5	$24.38	12.488%	$27.4246	$27.42	$27.40	$27.40
Purchase #6	$213.89	13.646%	$243.0774	$243.08	$243.10	$243.10
Purchase #7	$119.46	9.272%	$130.5363	$130.54	$130.55	$130.50
7 purchase totals =	$962.17		$1,053.5617	$1,053.57	$1,053.55	$1,053.50