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	$205.82	9.632%	$225.6446	$225.64	$225.65	$225.60
Purchase #2	$29.26	7.662%	$31.5019	$31.50	$31.50	$31.50
Purchase #3	$57.31	3.216%	$59.1531	$59.15	$59.15	$59.20
Purchase #4	$249.26	12.513%	$280.4499	$280.45	$280.45	$280.40
Purchase #5	$248.84	8.814%	$270.7728	$270.77	$270.75	$270.80
Purchase #6	$26.77	5.716%	$28.3002	$28.30	$28.30	$28.30
Purchase #7	$76.78	11.420%	$85.5483	$85.55	$85.55	$85.50
7 purchase totals =	$894.04		$981.3708	$981.36	$981.35	$981.30