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	$46.50	7.844%	$50.1475	$50.15	$50.15	$50.10
Purchase #2	$232.47	13.274%	$263.3281	$263.33	$263.35	$263.30
Purchase #3	$164.83	4.507%	$172.2589	$172.26	$172.25	$172.30
Purchase #4	$179.61	8.473%	$194.8284	$194.83	$194.85	$194.80
Purchase #5	$232.46	13.510%	$263.8653	$263.87	$263.85	$263.90
Purchase #6	$89.44	10.780%	$99.0816	$99.08	$99.10	$99.10
Purchase #7	$143.83	3.531%	$148.9086	$148.91	$148.90	$148.90
7 purchase totals =	$1,089.14		$1,192.4184	$1,192.43	$1,192.45	$1,192.40