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	$119.93	6.678%	$127.9389	$127.94	$127.95	$127.90
Purchase #2	$99.77	10.133%	$109.8797	$109.88	$109.90	$109.90
Purchase #3	$94.61	5.763%	$100.0624	$100.06	$100.05	$100.10
Purchase #4	$33.96	10.560%	$37.5462	$37.55	$37.55	$37.50
Purchase #5	$128.85	3.723%	$133.6471	$133.65	$133.65	$133.60
Purchase #6	$133.28	4.366%	$139.099	$139.10	$139.10	$139.10
Purchase #7	$30.96	7.711%	$33.3473	$33.35	$33.35	$33.30
7 purchase totals =	$641.36		$681.5206	$681.53	$681.55	$681.40