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	$40.96	6.557%	$43.6457	$43.65	$43.65	$43.60
Purchase #2	$31.90	4.525%	$33.3435	$33.34	$33.35	$33.30
Purchase #3	$135.78	4.181%	$141.457	$141.46	$141.45	$141.50
Purchase #4	$11.27	11.104%	$12.5214	$12.52	$12.50	$12.50
Purchase #5	$115.45	7.308%	$123.8871	$123.89	$123.90	$123.90
Purchase #6	$228.69	3.321%	$236.2848	$236.28	$236.30	$236.30
Purchase #7	$22.93	4.454%	$23.9513	$23.95	$23.95	$24.00
7 purchase totals =	$586.98		$615.0908	$615.09	$615.10	$615.10