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	$243.36	11.844%	$272.1836	$272.18	$272.20	$272.20
Purchase #2	$228.27	6.726%	$243.6234	$243.62	$243.60	$243.60
Purchase #3	$108.54	10.466%	$119.8998	$119.90	$119.90	$119.90
Purchase #4	$185.29	5.126%	$194.788	$194.79	$194.80	$194.80
Purchase #5	$83.85	11.766%	$93.7158	$93.72	$93.70	$93.70
Purchase #6	$180.86	5.180%	$190.2285	$190.23	$190.25	$190.20
Purchase #7	$82.60	10.121%	$90.9599	$90.96	$90.95	$91.00
7 purchase totals =	$1,112.77		$1,205.3990	$1,205.40	$1,205.40	$1,205.40