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	$138.41	10.584%	$153.0593	$153.06	$153.05	$153.10
Purchase #2	$88.89	13.534%	$100.9204	$100.92	$100.90	$100.90
Purchase #3	$79.92	6.840%	$85.3865	$85.39	$85.40	$85.40
Purchase #4	$97.72	6.640%	$104.2086	$104.21	$104.20	$104.20
Purchase #5	$84.46	5.753%	$89.319	$89.32	$89.30	$89.30
Purchase #6	$164.77	9.604%	$180.5945	$180.59	$180.60	$180.60
Purchase #7	$235.73	10.380%	$260.1988	$260.20	$260.20	$260.20
7 purchase totals =	$889.90		$973.6871	$973.69	$973.65	$973.70