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	$240.69	7.318%	$258.3037	$258.30	$258.30	$258.30
Purchase #2	$105.90	12.139%	$118.7552	$118.76	$118.75	$118.80
Purchase #3	$69.52	9.105%	$75.8498	$75.85	$75.85	$75.80
Purchase #4	$11.61	6.863%	$12.4068	$12.41	$12.40	$12.40
Purchase #5	$136.89	10.689%	$151.5222	$151.52	$151.50	$151.50
Purchase #6	$130.45	7.449%	$140.1672	$140.17	$140.15	$140.20
Purchase #7	$168.84	7.375%	$181.292	$181.29	$181.30	$181.30
7 purchase totals =	$863.90		$938.2969	$938.30	$938.25	$938.30