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	$131.47	8.189%	$142.2361	$142.24	$142.25	$142.20
Purchase #2	$51.45	5.837%	$54.4531	$54.45	$54.45	$54.50
Purchase #3	$27.45	12.362%	$30.8434	$30.84	$30.85	$30.80
Purchase #4	$227.67	7.826%	$245.4875	$245.49	$245.50	$245.50
Purchase #5	$18.39	9.361%	$20.1115	$20.11	$20.10	$20.10
Purchase #6	$49.41	12.317%	$55.4958	$55.50	$55.50	$55.50
Purchase #7	$52.51	5.156%	$55.2174	$55.22	$55.20	$55.20
7 purchase totals =	$558.35		$603.8448	$603.85	$603.85	$603.80