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	$55.32	7.234%	$59.3218	$59.32	$59.30	$59.30
Purchase #2	$226.81	4.268%	$236.4903	$236.49	$236.50	$236.50
Purchase #3	$73.76	9.564%	$80.8144	$80.81	$80.80	$80.80
Purchase #4	$127.45	8.788%	$138.6503	$138.65	$138.65	$138.70
Purchase #5	$200.76	10.303%	$221.4443	$221.44	$221.45	$221.40
Purchase #6	$84.75	4.781%	$88.8019	$88.80	$88.80	$88.80
Purchase #7	$172.96	13.344%	$196.0398	$196.04	$196.05	$196.00
7 purchase totals =	$941.81		$1,021.5628	$1,021.55	$1,021.55	$1,021.50