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	$178.66	6.170%	$189.6833	$189.68	$189.70	$189.70
Purchase #2	$72.99	7.506%	$78.4686	$78.47	$78.45	$78.50
Purchase #3	$131.29	5.558%	$138.5871	$138.59	$138.60	$138.60
Purchase #4	$206.29	7.692%	$222.1578	$222.16	$222.15	$222.20
Purchase #5	$142.88	9.264%	$156.1164	$156.12	$156.10	$156.10
Purchase #6	$35.72	10.834%	$39.5899	$39.59	$39.60	$39.60
Purchase #7	$248.94	4.498%	$260.1373	$260.14	$260.15	$260.10
7 purchase totals =	$1,016.77		$1,084.7404	$1,084.75	$1,084.75	$1,084.80