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	$130.64	4.419%	$136.413	$136.41	$136.40	$136.40
Purchase #2	$141.94	6.162%	$150.6863	$150.69	$150.70	$150.70
Purchase #3	$134.44	11.862%	$150.3873	$150.39	$150.40	$150.40
Purchase #4	$101.32	12.578%	$114.064	$114.06	$114.05	$114.10
Purchase #5	$132.38	6.451%	$140.9198	$140.92	$140.90	$140.90
Purchase #6	$6.50	7.634%	$6.9962	$7.00	$7.00	$7.00
Purchase #7	$80.31	11.102%	$89.226	$89.23	$89.25	$89.20
7 purchase totals =	$727.53		$788.6926	$788.70	$788.70	$788.70