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	$103.42	5.507%	$109.1153	$109.12	$109.10	$109.10
Purchase #2	$42.45	3.397%	$43.892	$43.89	$43.90	$43.90
Purchase #3	$55.60	9.416%	$60.8353	$60.84	$60.85	$60.80
Purchase #4	$119.82	11.268%	$133.3213	$133.32	$133.30	$133.30
Purchase #5	$117.66	11.696%	$131.4215	$131.42	$131.40	$131.40
Purchase #6	$249.57	5.673%	$263.7281	$263.73	$263.75	$263.70
Purchase #7	$164.73	3.538%	$170.5581	$170.56	$170.55	$170.60
7 purchase totals =	$853.25		$912.8716	$912.88	$912.85	$912.80