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	$139.61	3.772%	$144.8761	$144.88	$144.90	$144.90
Purchase #2	$47.94	7.152%	$51.3687	$51.37	$51.35	$51.40
Purchase #3	$77.89	13.833%	$88.6645	$88.66	$88.65	$88.70
Purchase #4	$100.47	9.219%	$109.7323	$109.73	$109.75	$109.70
Purchase #5	$76.44	5.826%	$80.8934	$80.89	$80.90	$80.90
Purchase #6	$180.78	4.773%	$189.4086	$189.41	$189.40	$189.40
Purchase #7	$43.83	11.305%	$48.785	$48.79	$48.80	$48.80
7 purchase totals =	$666.96		$713.7286	$713.73	$713.75	$713.80