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	$118.83	12.735%	$133.963	$133.96	$133.95	$134.00
Purchase #2	$60.42	12.204%	$67.7937	$67.79	$67.80	$67.80
Purchase #3	$82.46	8.110%	$89.1475	$89.15	$89.15	$89.10
Purchase #4	$44.46	3.805%	$46.1517	$46.15	$46.15	$46.20
Purchase #5	$86.52	11.230%	$96.2362	$96.24	$96.25	$96.20
Purchase #6	$120.72	10.480%	$133.3715	$133.37	$133.35	$133.40
Purchase #7	$225.88	6.466%	$240.4854	$240.49	$240.50	$240.50
7 purchase totals =	$739.29		$807.1490	$807.15	$807.15	$807.20