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	$137.33	8.371%	$148.8259	$148.83	$148.85	$148.80
Purchase #2	$54.49	9.178%	$59.4911	$59.49	$59.50	$59.50
Purchase #3	$83.55	8.252%	$90.4445	$90.44	$90.45	$90.40
Purchase #4	$27.28	7.314%	$29.2753	$29.28	$29.30	$29.30
Purchase #5	$59.35	8.644%	$64.4802	$64.48	$64.50	$64.50
Purchase #6	$177.83	6.167%	$188.7968	$188.80	$188.80	$188.80
Purchase #7	$250.93	7.114%	$268.7812	$268.78	$268.80	$268.80
7 purchase totals =	$790.76		$850.0950	$850.10	$850.20	$850.10