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	$75.63	3.239%	$78.0797	$78.08	$78.10	$78.10
Purchase #2	$62.43	8.139%	$67.5112	$67.51	$67.50	$67.50
Purchase #3	$54.60	8.704%	$59.3524	$59.35	$59.35	$59.40
Purchase #4	$57.73	10.537%	$63.813	$63.81	$63.80	$63.80
Purchase #5	$144.47	7.588%	$155.4324	$155.43	$155.45	$155.40
Purchase #6	$98.45	3.603%	$101.9972	$102.00	$102.00	$102.00
Purchase #7	$73.42	5.207%	$77.243	$77.24	$77.25	$77.20
7 purchase totals =	$566.73		$603.4289	$603.42	$603.45	$603.40