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	$108.66	13.182%	$122.9836	$122.98	$123.00	$123.00
Purchase #2	$188.65	10.836%	$209.0921	$209.09	$209.10	$209.10
Purchase #3	$151.50	11.841%	$169.4391	$169.44	$169.45	$169.40
Purchase #4	$169.87	12.803%	$191.6185	$191.62	$191.60	$191.60
Purchase #5	$72.32	7.378%	$77.6558	$77.66	$77.65	$77.70
Purchase #6	$171.67	10.172%	$189.1323	$189.13	$189.15	$189.10
Purchase #7	$123.91	13.216%	$140.2859	$140.29	$140.30	$140.30
7 purchase totals =	$986.58		$1,100.2073	$1,100.21	$1,100.25	$1,100.20