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	$18.87	4.835%	$19.7824	$19.78	$19.80	$19.80
Purchase #2	$101.91	12.712%	$114.8648	$114.86	$114.85	$114.90
Purchase #3	$161.59	6.269%	$171.7201	$171.72	$171.70	$171.70
Purchase #4	$142.68	12.644%	$160.7205	$160.72	$160.70	$160.70
Purchase #5	$67.41	4.299%	$70.308	$70.31	$70.30	$70.30
Purchase #6	$73.40	9.428%	$80.3202	$80.32	$80.30	$80.30
Purchase #7	$184.60	3.711%	$191.4505	$191.45	$191.45	$191.50
7 purchase totals =	$750.46		$809.1665	$809.16	$809.10	$809.20