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	$118.90	9.848%	$130.6093	$130.61	$130.60	$130.60
Purchase #2	$223.95	7.276%	$240.2446	$240.24	$240.25	$240.20
Purchase #3	$215.70	12.835%	$243.3851	$243.39	$243.40	$243.40
Purchase #4	$60.90	9.608%	$66.7513	$66.75	$66.75	$66.80
Purchase #5	$129.72	11.569%	$144.7273	$144.73	$144.75	$144.70
Purchase #6	$77.50	6.232%	$82.3298	$82.33	$82.35	$82.30
Purchase #7	$18.35	9.201%	$20.0384	$20.04	$20.05	$20.00
7 purchase totals =	$845.02		$928.0858	$928.09	$928.15	$928.00