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	$250.39	8.664%	$272.0838	$272.08	$272.10	$272.10
Purchase #2	$185.85	12.459%	$209.0051	$209.01	$209.00	$209.00
Purchase #3	$90.87	10.514%	$100.4241	$100.42	$100.40	$100.40
Purchase #4	$178.69	13.829%	$203.401	$203.40	$203.40	$203.40
Purchase #5	$103.72	6.498%	$110.4597	$110.46	$110.45	$110.50
Purchase #6	$145.26	12.113%	$162.8553	$162.86	$162.85	$162.90
Purchase #7	$56.55	3.214%	$58.3675	$58.37	$58.35	$58.40
7 purchase totals =	$1,011.33		$1,116.5965	$1,116.60	$1,116.55	$1,116.70