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	$96.34	12.149%	$108.0443	$108.04	$108.05	$108.00
Purchase #2	$200.67	10.507%	$221.7544	$221.75	$221.75	$221.80
Purchase #3	$189.86	13.449%	$215.3943	$215.39	$215.40	$215.40
Purchase #4	$81.56	8.633%	$88.6011	$88.60	$88.60	$88.60
Purchase #5	$114.86	7.711%	$123.7169	$123.72	$123.70	$123.70
Purchase #6	$120.74	8.314%	$130.7783	$130.78	$130.80	$130.80
Purchase #7	$106.56	6.313%	$113.2871	$113.29	$113.30	$113.30
7 purchase totals =	$910.59		$1,001.5764	$1,001.57	$1,001.60	$1,001.60