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	$218.50	11.705%	$244.0754	$244.08	$244.10	$244.10
Purchase #2	$31.34	13.309%	$35.511	$35.51	$35.50	$35.50
Purchase #3	$21.51	12.841%	$24.2721	$24.27	$24.25	$24.30
Purchase #4	$131.90	10.497%	$145.7455	$145.75	$145.75	$145.70
Purchase #5	$146.54	13.290%	$166.0152	$166.02	$166.00	$166.00
Purchase #6	$154.97	3.167%	$159.8779	$159.88	$159.90	$159.90
Purchase #7	$208.57	6.565%	$222.2626	$222.26	$222.25	$222.30
7 purchase totals =	$913.33		$997.7597	$997.77	$997.75	$997.80