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	$38.29	11.405%	$42.657	$42.66	$42.65	$42.70
Purchase #2	$114.41	3.187%	$118.0562	$118.06	$118.05	$118.10
Purchase #3	$183.89	5.614%	$194.2136	$194.21	$194.20	$194.20
Purchase #4	$250.39	3.615%	$259.4416	$259.44	$259.45	$259.40
Purchase #5	$145.67	7.170%	$156.1145	$156.11	$156.10	$156.10
Purchase #6	$143.48	4.799%	$150.3656	$150.37	$150.35	$150.40
Purchase #7	$18.33	8.342%	$19.8591	$19.86	$19.85	$19.90
7 purchase totals =	$894.46		$940.7076	$940.71	$940.65	$940.80