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	$37.72	4.156%	$39.2876	$39.29	$39.30	$39.30
Purchase #2	$82.69	4.465%	$86.3821	$86.38	$86.40	$86.40
Purchase #3	$191.88	3.805%	$199.181	$199.18	$199.20	$199.20
Purchase #4	$179.32	9.334%	$196.0577	$196.06	$196.05	$196.10
Purchase #5	$228.98	8.495%	$248.4319	$248.43	$248.45	$248.40
Purchase #6	$180.89	9.733%	$198.496	$198.50	$198.50	$198.50
Purchase #7	$248.52	5.863%	$263.0907	$263.09	$263.10	$263.10
7 purchase totals =	$1,150.00		$1,230.9270	$1,230.93	$1,231.00	$1,231.00