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	$36.34	11.505%	$40.5209	$40.52	$40.50	$40.50
Purchase #2	$46.80	3.228%	$48.3107	$48.31	$48.30	$48.30
Purchase #3	$187.63	11.132%	$208.517	$208.52	$208.50	$208.50
Purchase #4	$119.37	10.103%	$131.43	$131.43	$131.45	$131.40
Purchase #5	$127.84	10.307%	$141.0165	$141.02	$141.00	$141.00
Purchase #6	$45.55	5.842%	$48.211	$48.21	$48.20	$48.20
Purchase #7	$78.35	10.179%	$86.3252	$86.33	$86.35	$86.30
7 purchase totals =	$641.88		$704.3313	$704.34	$704.30	$704.20