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	$129.53	7.593%	$139.3652	$139.37	$139.35	$139.40
Purchase #2	$29.88	3.810%	$31.0184	$31.02	$31.00	$31.00
Purchase #3	$67.41	6.243%	$71.6184	$71.62	$71.60	$71.60
Purchase #4	$120.86	13.784%	$137.5193	$137.52	$137.50	$137.50
Purchase #5	$98.27	9.615%	$107.7187	$107.72	$107.70	$107.70
Purchase #6	$191.88	9.363%	$209.8457	$209.85	$209.85	$209.80
Purchase #7	$120.91	11.204%	$134.4568	$134.46	$134.45	$134.50
7 purchase totals =	$758.74		$831.5425	$831.56	$831.45	$831.50