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	$100.98	10.843%	$111.9293	$111.93	$111.95	$111.90
Purchase #2	$160.85	11.304%	$179.0325	$179.03	$179.05	$179.00
Purchase #3	$115.48	10.771%	$127.9184	$127.92	$127.90	$127.90
Purchase #4	$195.87	12.552%	$220.4556	$220.46	$220.45	$220.50
Purchase #5	$215.61	4.606%	$225.541	$225.54	$225.55	$225.50
Purchase #6	$77.88	8.184%	$84.2537	$84.25	$84.25	$84.30
Purchase #7	$171.65	10.282%	$189.2991	$189.30	$189.30	$189.30
7 purchase totals =	$1,038.32		$1,138.4296	$1,138.43	$1,138.45	$1,138.40