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	$33.37	10.301%	$36.8074	$36.81	$36.80	$36.80
Purchase #2	$71.78	12.177%	$80.5207	$80.52	$80.50	$80.50
Purchase #3	$55.62	6.575%	$59.277	$59.28	$59.30	$59.30
Purchase #4	$174.58	12.257%	$195.9783	$195.98	$196.00	$196.00
Purchase #5	$168.80	6.560%	$179.8733	$179.87	$179.85	$179.90
Purchase #6	$181.68	8.566%	$197.2427	$197.24	$197.25	$197.20
Purchase #7	$138.59	8.839%	$150.84	$150.84	$150.85	$150.80
7 purchase totals =	$824.42		$900.5394	$900.54	$900.55	$900.50