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	$9.99	4.410%	$10.4306	$10.43	$10.45	$10.40
Purchase #2	$222.57	12.276%	$249.8927	$249.89	$249.90	$249.90
Purchase #3	$93.64	5.451%	$98.7443	$98.74	$98.75	$98.70
Purchase #4	$72.72	13.352%	$82.4296	$82.43	$82.45	$82.40
Purchase #5	$96.31	6.765%	$102.8254	$102.83	$102.85	$102.80
Purchase #6	$29.99	3.482%	$31.0343	$31.03	$31.05	$31.00
Purchase #7	$199.65	11.340%	$222.2903	$222.29	$222.30	$222.30
7 purchase totals =	$724.87		$797.6472	$797.64	$797.75	$797.50