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	$103.40	3.870%	$107.4016	$107.40	$107.40	$107.40
Purchase #2	$84.46	8.722%	$91.8266	$91.83	$91.85	$91.80
Purchase #3	$177.47	7.267%	$190.3667	$190.37	$190.35	$190.40
Purchase #4	$45.34	7.535%	$48.7564	$48.76	$48.75	$48.80
Purchase #5	$154.75	9.789%	$169.8985	$169.90	$169.90	$169.90
Purchase #6	$59.49	6.418%	$63.3081	$63.31	$63.30	$63.30
Purchase #7	$173.46	13.390%	$196.6863	$196.69	$196.70	$196.70
7 purchase totals =	$798.37		$868.2442	$868.26	$868.25	$868.30