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	$159.57	7.218%	$171.0878	$171.09	$171.10	$171.10
Purchase #2	$130.45	12.257%	$146.4393	$146.44	$146.45	$146.40
Purchase #3	$98.81	12.868%	$111.5249	$111.52	$111.50	$111.50
Purchase #4	$20.57	6.569%	$21.9212	$21.92	$21.90	$21.90
Purchase #5	$98.40	10.793%	$109.0203	$109.02	$109.00	$109.00
Purchase #6	$104.77	9.411%	$114.6299	$114.63	$114.65	$114.60
Purchase #7	$202.32	6.449%	$215.3676	$215.37	$215.35	$215.40
7 purchase totals =	$814.89		$889.9910	$889.99	$889.95	$889.90