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	$39.25	9.205%	$42.863	$42.86	$42.85	$42.90
Purchase #2	$192.48	6.750%	$205.4724	$205.47	$205.45	$205.50
Purchase #3	$114.79	10.704%	$127.0771	$127.08	$127.10	$127.10
Purchase #4	$128.63	7.103%	$137.7666	$137.77	$137.75	$137.80
Purchase #5	$128.53	6.254%	$136.5683	$136.57	$136.55	$136.60
Purchase #6	$55.85	7.236%	$59.8913	$59.89	$59.90	$59.90
Purchase #7	$94.35	10.175%	$103.9501	$103.95	$103.95	$104.00
7 purchase totals =	$753.88		$813.5888	$813.59	$813.55	$813.80