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	$100.27	3.562%	$103.8416	$103.84	$103.85	$103.80
Purchase #2	$98.29	4.724%	$102.9332	$102.93	$102.95	$102.90
Purchase #3	$85.81	9.259%	$93.7551	$93.76	$93.75	$93.80
Purchase #4	$223.59	8.266%	$242.0719	$242.07	$242.05	$242.10
Purchase #5	$79.47	11.777%	$88.8292	$88.83	$88.85	$88.80
Purchase #6	$178.68	11.108%	$198.5278	$198.53	$198.55	$198.50
Purchase #7	$131.87	5.510%	$139.136	$139.14	$139.15	$139.10
7 purchase totals =	$897.98		$969.0948	$969.10	$969.15	$969.00