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	$227.90	5.310%	$240.0015	$240.00	$240.00	$240.00
Purchase #2	$216.32	9.700%	$237.303	$237.30	$237.30	$237.30
Purchase #3	$241.51	12.154%	$270.8631	$270.86	$270.85	$270.90
Purchase #4	$209.39	9.111%	$228.4675	$228.47	$228.45	$228.50
Purchase #5	$49.74	7.401%	$53.4213	$53.42	$53.40	$53.40
Purchase #6	$159.47	3.167%	$164.5204	$164.52	$164.50	$164.50
Purchase #7	$30.63	12.286%	$34.3932	$34.39	$34.40	$34.40
7 purchase totals =	$1,134.96		$1,228.9700	$1,228.96	$1,228.90	$1,229.00