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	$27.33	6.487%	$29.1029	$29.10	$29.10	$29.10
Purchase #2	$209.44	3.543%	$216.8605	$216.86	$216.85	$216.90
Purchase #3	$116.91	5.279%	$123.0817	$123.08	$123.10	$123.10
Purchase #4	$242.46	12.136%	$271.8849	$271.88	$271.90	$271.90
Purchase #5	$213.88	13.164%	$242.0352	$242.04	$242.05	$242.00
Purchase #6	$116.74	10.103%	$128.5342	$128.53	$128.55	$128.50
Purchase #7	$91.72	12.309%	$103.0098	$103.01	$103.00	$103.00
7 purchase totals =	$1,018.48		$1,114.5092	$1,114.50	$1,114.55	$1,114.50