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	$134.83	10.161%	$148.5301	$148.53	$148.55	$148.50
Purchase #2	$88.35	12.308%	$99.2241	$99.22	$99.20	$99.20
Purchase #3	$162.67	10.721%	$180.1099	$180.11	$180.10	$180.10
Purchase #4	$224.75	6.578%	$239.5341	$239.53	$239.55	$239.50
Purchase #5	$48.85	5.400%	$51.4879	$51.49	$51.50	$51.50
Purchase #6	$30.59	10.466%	$33.7915	$33.79	$33.80	$33.80
Purchase #7	$89.83	7.771%	$96.8107	$96.81	$96.80	$96.80
7 purchase totals =	$779.87		$849.4883	$849.48	$849.50	$849.40