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	$139.57	11.653%	$155.8341	$155.83	$155.85	$155.80
Purchase #2	$25.73	5.459%	$27.1346	$27.13	$27.15	$27.10
Purchase #3	$82.32	10.280%	$90.7825	$90.78	$90.80	$90.80
Purchase #4	$95.32	8.692%	$103.6052	$103.61	$103.60	$103.60
Purchase #5	$190.44	11.758%	$212.8319	$212.83	$212.85	$212.80
Purchase #6	$83.91	5.272%	$88.3337	$88.33	$88.35	$88.30
Purchase #7	$189.43	11.610%	$211.4228	$211.42	$211.40	$211.40
7 purchase totals =	$806.72		$889.9448	$889.93	$890.00	$889.80