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	$93.46	12.558%	$105.1967	$105.20	$105.20	$105.20
Purchase #2	$39.97	6.605%	$42.61	$42.61	$42.60	$42.60
Purchase #3	$71.92	8.538%	$78.0605	$78.06	$78.05	$78.10
Purchase #4	$109.31	4.340%	$114.0541	$114.05	$114.05	$114.10
Purchase #5	$89.85	8.554%	$97.5358	$97.54	$97.55	$97.50
Purchase #6	$156.73	10.495%	$173.1788	$173.18	$173.20	$173.20
Purchase #7	$54.63	10.420%	$60.3224	$60.32	$60.30	$60.30
7 purchase totals =	$615.87		$670.9583	$670.96	$670.95	$671.00