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	$109.25	3.680%	$113.2704	$113.27	$113.25	$113.30
Purchase #2	$38.59	3.356%	$39.8851	$39.89	$39.90	$39.90
Purchase #3	$22.34	13.558%	$25.3689	$25.37	$25.35	$25.40
Purchase #4	$139.71	4.734%	$146.3239	$146.32	$146.30	$146.30
Purchase #5	$36.91	3.355%	$38.1483	$38.15	$38.15	$38.10
Purchase #6	$22.63	12.583%	$25.4775	$25.48	$25.50	$25.50
Purchase #7	$133.57	13.497%	$151.5979	$151.60	$151.60	$151.60
7 purchase totals =	$503.00		$540.0720	$540.08	$540.05	$540.10