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	$40.35	5.106%	$42.4103	$42.41	$42.40	$42.40
Purchase #2	$118.93	13.739%	$135.2698	$135.27	$135.25	$135.30
Purchase #3	$117.55	4.685%	$123.0572	$123.06	$123.05	$123.10
Purchase #4	$120.77	7.818%	$130.2118	$130.21	$130.20	$130.20
Purchase #5	$117.57	8.756%	$127.8644	$127.86	$127.85	$127.90
Purchase #6	$245.28	11.254%	$272.8838	$272.88	$272.90	$272.90
Purchase #7	$55.51	11.548%	$61.9203	$61.92	$61.90	$61.90
7 purchase totals =	$815.96		$893.6176	$893.61	$893.55	$893.70