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	$127.86	13.450%	$145.0572	$145.06	$145.05	$145.10
Purchase #2	$137.80	5.611%	$145.532	$145.53	$145.55	$145.50
Purchase #3	$39.71	7.118%	$42.5366	$42.54	$42.55	$42.50
Purchase #4	$91.41	7.505%	$98.2703	$98.27	$98.25	$98.30
Purchase #5	$64.93	3.524%	$67.2181	$67.22	$67.20	$67.20
Purchase #6	$157.94	5.727%	$166.9852	$166.99	$167.00	$167.00
Purchase #7	$174.55	6.625%	$186.1139	$186.11	$186.10	$186.10
7 purchase totals =	$794.20		$851.7133	$851.72	$851.70	$851.70