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	$131.49	12.490%	$147.9131	$147.91	$147.90	$147.90
Purchase #2	$245.39	10.797%	$271.8848	$271.88	$271.90	$271.90
Purchase #3	$242.96	13.840%	$276.5857	$276.59	$276.60	$276.60
Purchase #4	$160.50	7.794%	$173.0094	$173.01	$173.00	$173.00
Purchase #5	$20.26	6.284%	$21.5331	$21.53	$21.55	$21.50
Purchase #6	$150.96	6.373%	$160.5807	$160.58	$160.60	$160.60
Purchase #7	$34.97	13.209%	$39.5892	$39.59	$39.60	$39.60
7 purchase totals =	$986.53		$1,091.0960	$1,091.09	$1,091.15	$1,091.10