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	$99.25	10.423%	$109.5948	$109.59	$109.60	$109.60
Purchase #2	$69.57	3.475%	$71.9876	$71.99	$72.00	$72.00
Purchase #3	$246.76	3.804%	$256.1468	$256.15	$256.15	$256.10
Purchase #4	$40.79	9.651%	$44.7266	$44.73	$44.75	$44.70
Purchase #5	$68.28	5.514%	$72.045	$72.05	$72.05	$72.00
Purchase #6	$229.55	8.347%	$248.7105	$248.71	$248.70	$248.70
Purchase #7	$162.38	5.572%	$171.4278	$171.43	$171.45	$171.40
7 purchase totals =	$916.58		$974.6391	$974.65	$974.70	$974.50