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	$35.58	11.731%	$39.7539	$39.75	$39.75	$39.80
Purchase #2	$101.33	9.859%	$111.3201	$111.32	$111.30	$111.30
Purchase #3	$77.66	12.774%	$87.5803	$87.58	$87.60	$87.60
Purchase #4	$142.43	7.843%	$153.6008	$153.60	$153.60	$153.60
Purchase #5	$38.35	10.484%	$42.3706	$42.37	$42.35	$42.40
Purchase #6	$32.40	3.384%	$33.4964	$33.50	$33.50	$33.50
Purchase #7	$218.53	7.106%	$234.0587	$234.06	$234.05	$234.10
7 purchase totals =	$646.28		$702.1808	$702.18	$702.15	$702.30