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	$236.46	5.741%	$250.0352	$250.04	$250.05	$250.00
Purchase #2	$128.28	10.394%	$141.6134	$141.61	$141.60	$141.60
Purchase #3	$37.31	12.776%	$42.0767	$42.08	$42.10	$42.10
Purchase #4	$91.29	7.244%	$97.903	$97.90	$97.90	$97.90
Purchase #5	$78.48	7.575%	$84.4249	$84.42	$84.40	$84.40
Purchase #6	$221.45	7.275%	$237.5605	$237.56	$237.55	$237.60
Purchase #7	$106.46	4.774%	$111.5424	$111.54	$111.55	$111.50
7 purchase totals =	$899.73		$965.1561	$965.15	$965.15	$965.10