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	$224.55	6.392%	$238.9032	$238.90	$238.90	$238.90
Purchase #2	$174.47	8.715%	$189.6751	$189.68	$189.70	$189.70
Purchase #3	$225.32	5.795%	$238.3773	$238.38	$238.40	$238.40
Purchase #4	$127.82	13.719%	$145.3556	$145.36	$145.35	$145.40
Purchase #5	$73.86	11.188%	$82.1235	$82.12	$82.10	$82.10
Purchase #6	$71.93	13.300%	$81.4967	$81.50	$81.50	$81.50
Purchase #7	$34.47	7.648%	$37.1063	$37.11	$37.10	$37.10
7 purchase totals =	$932.42		$1,013.0377	$1,013.05	$1,013.05	$1,013.10