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	$87.36	3.280%	$90.2254	$90.23	$90.25	$90.20
Purchase #2	$93.32	5.801%	$98.7335	$98.73	$98.75	$98.70
Purchase #3	$105.89	12.151%	$118.7567	$118.76	$118.75	$118.80
Purchase #4	$95.25	11.123%	$105.8447	$105.84	$105.85	$105.80
Purchase #5	$7.90	8.654%	$8.5837	$8.58	$8.60	$8.60
Purchase #6	$230.78	13.788%	$262.5999	$262.60	$262.60	$262.60
Purchase #7	$145.27	3.767%	$150.7423	$150.74	$150.75	$150.70
7 purchase totals =	$765.77		$835.4862	$835.48	$835.55	$835.40