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	$45.91	11.581%	$51.2268	$51.23	$51.25	$51.20
Purchase #2	$153.37	10.314%	$169.1886	$169.19	$169.20	$169.20
Purchase #3	$91.46	8.586%	$99.3128	$99.31	$99.30	$99.30
Purchase #4	$146.96	4.217%	$153.1573	$153.16	$153.15	$153.20
Purchase #5	$71.37	9.280%	$77.9931	$77.99	$78.00	$78.00
Purchase #6	$155.29	6.289%	$165.0562	$165.06	$165.05	$165.10
Purchase #7	$123.33	8.288%	$133.5516	$133.55	$133.55	$133.60
7 purchase totals =	$787.69		$849.4864	$849.49	$849.50	$849.60