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	$149.86	5.150%	$157.5778	$157.58	$157.60	$157.60
Purchase #2	$123.59	11.123%	$137.3369	$137.34	$137.35	$137.30
Purchase #3	$189.41	5.306%	$199.4601	$199.46	$199.45	$199.50
Purchase #4	$58.90	7.169%	$63.1225	$63.12	$63.10	$63.10
Purchase #5	$82.85	7.869%	$89.3695	$89.37	$89.35	$89.40
Purchase #6	$55.88	9.522%	$61.2009	$61.20	$61.20	$61.20
Purchase #7	$90.41	13.816%	$102.901	$102.90	$102.90	$102.90
7 purchase totals =	$750.90		$810.9687	$810.97	$810.95	$811.00