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	$56.77	7.258%	$60.8904	$60.89	$60.90	$60.90
Purchase #2	$85.51	10.735%	$94.6895	$94.69	$94.70	$94.70
Purchase #3	$138.42	7.175%	$148.3516	$148.35	$148.35	$148.40
Purchase #4	$53.28	3.212%	$54.9914	$54.99	$55.00	$55.00
Purchase #5	$162.56	4.314%	$169.5728	$169.57	$169.55	$169.60
Purchase #6	$123.31	6.520%	$131.3498	$131.35	$131.35	$131.30
Purchase #7	$42.97	10.686%	$47.5618	$47.56	$47.55	$47.60
7 purchase totals =	$662.82		$707.4073	$707.40	$707.40	$707.50