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	$71.41	9.632%	$78.2882	$78.29	$78.30	$78.30
Purchase #2	$157.67	4.852%	$165.3201	$165.32	$165.30	$165.30
Purchase #3	$105.79	4.690%	$110.7516	$110.75	$110.75	$110.80
Purchase #4	$115.96	6.528%	$123.5299	$123.53	$123.55	$123.50
Purchase #5	$124.45	8.383%	$134.8826	$134.88	$134.90	$134.90
Purchase #6	$250.26	4.660%	$261.9221	$261.92	$261.90	$261.90
Purchase #7	$112.74	9.430%	$123.3714	$123.37	$123.35	$123.40
7 purchase totals =	$938.28		$998.0659	$998.06	$998.05	$998.10